Give 'em enough rope, but also provide clues and hints

You need to determine, by talking to the veteran jogadores, whether or not they are aware that they can flee if a fight is too much for them. Do this before the next session begins.

This danger in short cutting to Cragmaw (before you think they can handle it) needs to be shown in the shape of warnings, forebodings, rumors, and some physical evidence found (dead bodies, discarded equipment, etc) as they approach "the end" prematurely.

If they don't heed the clues, let them face a lethal encounter and ...

1. ... roll up new characters after the TPK or
2. ... awaken as prisoners of (pick an NPC) with their next challenge being ... how do we get out of here? ou

3. ... surprise you by succeeding against extremely long odds

   A reason I raise point 2 is that with new players, and given how swingy low level combat is, the option to proceed-on after failing is a way to encourage new players to learn as they play. So too is the party wipe: it really depends on your players.

If you have not yet discussed with them, out of character, whether or not a TPK may happen if they don't use their wits (in a general sense) then discussing this with the whole group before Session 2 begins is a good idea. You might call that a bit of out-of-character foreboding, but with new players being in the mix that is not necessarily a bad thing.

Option 2: transfer the knowledge to a different NPC

You can decide to not raise that point during the interrogation and have a different NPC, later on, provide the same info that the goblin has now. That information does not have to come to the players from this goblin. It can come from any NPC; you are the DM, pacing is within your area of control.

I just noticed that @Neewbie12345 covers this option in more detail so I won't elaborate further.

O que fizemos

We are nearing the end of LMoP now. I am a player, but I think I know the session 1 possible situation you are talking about. Here is what my DM did and it worked well:

The session 1 goblin we questioned was basically a dumb soldier who gave up partial details, but he really didn't know much.

After getting to town there were a lot of plot hooks for side quests, but there was a LOT of emphasis on the Red Brands and Glasstaff and motivation for us to handle the Red Brands since we really didn't have any leads on where Gundren was.

While going after Glasstaff and the Red Brands, we found another goblin who had been captured and tortured by the Red Brands. We rescued him and he was willing to give more details on how to get to Cragmaw.

Dumb goblins

As the DM, you can delay information until you are ready for the players to have it. Remember, goblins are typically pretty dumb and soldiers rarely have "big picture" information. Even with a natural 20, they can't give up information they don't have..

Not to worry, Cragmaw (Keep) Castle isn't the end of the adventure - it's where you find

Gundren and the map to the final location.

It triggers the end game but it isn't the end game. It is the first real step on the way to the final destination -

Wave Echo Cave.

Since you've completed the first session I'd wager that you're dealing with the goblin named Yeemik (or one of his unnamed pals) in Cragmaw Hideout. Yeemik giving them this information doesn't necessarily mean they'll run straight there!

Based on the adventure as written, it expects the party to be at third level when they arrive at Cragmaw Castle so it would be a difficult fight for a party of lower level. But that doesn't mean they can't or shouldn't do it! It could be a triumphant win or a devastating defeat.

In my experience, players are prone to rush into whatever plot hook has most recently been offered to them when they aren't sure what else they should do.

So, show them what options they have while letting them feel like they are in control of their destiny:

Allow the party to head for Cragmaw Castle

Danger lurks along the Triboar Trail...

• Do justice to travelling to the location by peppering it with random encounters along the way - this will help the players level up and may give them an indication that it would be nice to go to town for supplies.

• Encounter a group of Redbrand reinforcements on the Triboar Trail who on their way to Phandalin - the party can overhear them speaking about something to pique their interest and bring that plot into the players immediate focus like:

• the Black Spider or Glasstaff

Use Yeemik

Yeemik just wants to get out of this situation alive, preferably without disclosing the actual location of his friends and comrades.

• Send them on a wild goose chase! Yeemik (the goblin) only has very vague knowledge of where Cragmaw Castle is, he is not as reliable an information source as the party may expect! He could send them into an ambush or just completely the wrong place.
• Require a guide - Yeemik (the goblin) insists on going with them as a guide and then have him escape during the travel!
• If Yeemik betrays them, have him reappear later in the adventure - he's now a minor villain who they have a vested interest in punishing.

Gently nudge them in the direction you'd like them to go using Sildar Hallwinter

Sildar can provide a more measured and logical reaction to this information. He has his own attachments to Gundren and his own business in Phandalin.

• Sildar wants to go to Phandalin because he has business to attend to for the Lord's Alliance - in the text it says he will offer the characters 50GP to accompany him back. It's on the way to Cragmaw Castle (sort of, but not really) so only a minor detour - it could be an easy sell!
• Sildar suggests they go Phandalin and regroup, rest up and gather supplies and then they can head to Cragmaw Castle. Sildar wants to see Gundren alive as much as anyone else, they should trust his judgement.
• If they go with him to Phandalin, give them a reason to stay! You could immediately introduce the Redbrands either by a direct encounter or some sort of emotional plea from the townsfolk.
• If they refuse, Sildar goes on his own and can be a little less friendly next time they see him - or will refuse to help them in future.

Scale the Cragmaw Castle encounter levemente

It can still be hard without being deadly.

• Reduce the number of opponents by one or two per room. Adjust this on the fly.

• Don't include the returning warband unless the characters have triumphed by a landslide.

The adventure doesn't indicate that the PCs know the exact location of the castle, just the general location. As such, when I run it and they rush it, I simply say they need a guide to find it, and the best guide is at Redbrand. This gives them more interaction and more chance to level up.

That said, if they find some way to bypass that, a skilled party of 6 or so level 2s can handle the keep, especially if they use ambushes from the ruined north side.

I am running the campaign right now, and I also had a similar issue. I just made the goblin not know as much as the text says; he knows the castle is off the Triboar Trail, but that could be anywhere within hundreds of miles of forest.

I made the Redbrand threat quite a problem, especially by using the in-town encounter and really laying on the rewards possible for dealing with them/finding Iarno. Now my players are looking for the Castle by way of finding the Druid at Thundertree, I figured after dealing with the Redbrands, dealing with a young green dragon, and with random encounters; they would be level three and plenty strong to deal with the Castle.

Remember, you are the DM and you can choose to add things to the adventure that makes it take longer or shorter depending. Maybe there is a rival band jealous that the party is attempting to find the lost mine and decides to attack Phandalin or the party itself, maybe they escape and need to be hunted down. Maybe during their time on the trail a traveling merchant is attacked by bandits and needs the party's assistance.

Cragmaw Keep isn't the end of the campaign.

In my group (I was a player), we went to the goblin hideout after the ambush, then to town, and the next stop was Cragmaw Keep already. By the time we were done with the keep, we'd maybe finished 1/4, or at most 1/3 of the campaign (session-wise).

Hence, you don't have to worry at all. I do believe that our DM made the keep a little less difficult, so you might want to think about that - but since most encounters in LMOP are rather easy (imho), you might also be just fine, depending on how strategic your group plays. Note: in our campaign, I was playing a barbarian, not one of the pregenerated characters, so that might have had a significant impact on the difficulty, considering that barbarians are one of the strongest classes at low levels.