I am a new DM and I ask myself, are there restrictions to resting?
Can the PCs decide to take a long rest in a goblin cave after the first group of goblins beat them to a mostly bloody pulp, because the PCs rolled so bad? The cave is not huge and I can't imagine the rest of the goblins sitting still for half a day.
So I would only allow a short rest, but then the group does not recover as much hit points/spells and might wipe in the next fight.
Any solutions?
I'm going to address this in two ways. The first is with the resting rules as presented in the PHB/Starter, and the second is to have a short chat about the alternative resting rules as laid out in the DMG.
First and foremost, we need to talk about how resting works in 5e. Short rests have a timeframe of 1 hour, and long rests have a timeframe of 8 hours. This means that in most scenarios you only want to take short rests in dungeons, and to do so sparingly. To some degree, this is the point of the time frames being this long, dungeons are designed to drain resources from PCs so that final battles in dungeons are meaningful, at least for some value of meaningful.
However, each party is going to have their own comfort level with how many resources are expended at certain points in the dungeon and how much rest their heroes need. How much trouble they have finding a safe spot to rest (or how effective their watches are if they do take a long rest) is up to you as the DM. I can tell you that the first group of players I ran through the starter was feeling mighty uncomfortable by the time they cleared out the second or third encounter, several PCs had nearly died and it seemed like a really good spot in the adventure to take a long rest. How you adjudicate this as a DM is sort of up to you. Long rests are not completely interrupted if a fight breaks out, so it's within your rights to let your PCs rest, but to spring an encounter on them while they are sleeping (though, if you plan to do this, it doesn't hurt to let them know either implicitly or explicitly, that resting here is not safe and may end up triggering an encounter over night). If you really don't want them resting in a certain spot, let them know, they see patrols, or traces of them that seem to pass regularly, or whatever.
That said, in many dungeons, there is no reason that you can't simply let yourself out into the wilderness to go have a nap. This is a possibility in the first cave in the starter set. A 15 minute hike into the woods should reveal a reasonable camp site that won't get discovered by the goblins.
Finally, there are alternative resting rules. They basically allow you to adjust the amount of time short and long rests take in order to defray certain costs. For instance the easiest one changes short rests to 5 minutes and long rests to an hour. This is probably to extreme for your game at this time, but, just the same, it doesn't hurt to modify the time frames to get the game you want to play (these are completely laid out in DMG 267-268).
So, basically, the advise that I'll give you is decide the style of game you want, decide how hurt you want your players to be, and dictate (with some input from them to be sure) how they should be resting based on the style of game you are playing. In the starter (And this is what I've done in my 5e games, including the starter), don't be too hard on your characters for wanting to take a rest, it's not hugely consequential, and they'll probably have more fun if their toys are all available for the rest of the session.
It's less a matter of "are the players allowed to rest here" and more a matter of "what will happen if the players rest here". Technically speaking, players can take a short or long rest whenever and wherever they want. However, the world will keep going around them. The adventure doesn't stop just because you want a nap, basically.
Try to think of it like how a realistic world would work. If a group of people entered a cave and murdered the goblins there, then what would happen when they tried to sleep in that cave? Likely, they'd have a little bit of time to rest before the rest of the goblins in the cave attacked them. Or maybe the goblins would set up defenses further in that would make the next fight harder.
It wouldn't be unreasonable for the players to get a short rest before moving on, but taking a long rest should probably have some consequences. They can try to take that rest, but they shouldn't be terribly surprised when they are ambushed in the middle of it.
I was discussing the matter with my DM. He informed me that the DMG states (alas, I don't have a copy, or I'd provide a page) that the classes are designed and balanced with two short rests as a daily norm.
To occasionally have days with only one short rest--or three short rests for that matter--is probably not game-breaking, but it does affect class balance in a small way, as some classes have more or fewer abilities that recharge during a short rest.
If the group frequently requests more long rests than is normal for the game balance, there are a few things to consider:
First, and foremost, party enjoyment is the reason we play. Unless your campaign is meant to be gritty, challenging, and generally accepting of total party KO, then it is best to be lenient and forgiving when encounters go dramatically awry.
The DM may grant some rest and reprieve, provide means of escape, fast-forward the story to another date and time, or otherwise narrate her way around the challenge. If appropriate, the DM may simply grant that the party "come up for air" and return to the scenario later, refreshed.
Alternatively, the players may set up watches, allowing some of them a short rest while others stand guard. This kind of "cautious short rest" may be an effective tool to grant necessary reprieve while inviting the players to make choices about who gets the benefits. This approach should only be considered if your players are open to making tough choices.
If it should ever be the case that the DM wants to challenge the players or that she considers her players to be taking too many rests, she could allow a short rest, only to interrupt it with a random encounter. This can be a device to communicate that short rests are not an entitlement; however, in this scenario, your players desperately need to regroup, so this response may not be welcome.
The DM may also modify the difficulty of upcoming encounters. Sometimes hitting that sweet spot of providing a good challenge while not steamrolling over players can be challenging, and DMs should be prepared to modify the encounters if their planning went wrong or the dice rolled too unfavorably.
At the end of the day, the DM and the players cooperatively choose the kind of game they want to play. I would advise that the DM only deny short rests in the event that the daily quota is exceeded and the encounter design is intended to provoke a sense of urgency.
Cheers!
