Low level PCs are fragile.
Depending on class and CON score they have between 6 and 15hp. The wolves can do a maximum of 10hp. This can drop a character in a single hit and even the best will only last 2 or 3. On a critical hit, insta-death is a distinct possibility. The bugbear a little bit later is even worse (max 18 damage).
This is a deliberate design decision for 5th edition; it is tougher than 4th, about on par with 2, 3 & 3.5 (at low levels - easier at high levels) and much, much more lenient than 0 & 1. With its bounded rationality aspect, PC death is always on the table when fighting monsters that can deal damage in the same order as the character's hp.
In order to die you must:
- Take damage greater than your current hit points (which can never be less than 0) plus your maximum hit points in a single attack/spell/damaging event. For a first level character on full hp this can range from 12 to 30 - pretty big but doable (at the lower end) by some monsters in the starter set. If the PC is on less than max hp (down to 0) this can be much easier. As the PCs gain levels their max hp increases so this way of dying becomes much less likely.
- Be reduced to 0hp and fail 3 death saving throws before stabilizing or being healed. Being hit again counts as a saving throw failure or 2 for a critical hit.
Character death is and (in my opinion) should be a real and distinct possibility - nothing ventured, nothing gained. Player's should regard combat as a situation of mortal peril - this encourages them to find non-combat solutions to the problem. Players who recklessly run their characters into combat are going to die and die often.
From memory, the wolves in question are chained in a den and the PCs have several options ranging from don't go in there, to feeding and befriending them, to standing outside and shooting the wolves (the wolves can break the chain but this should still give them a big advantage).
Are you playing fair?
First off, remember you don't have to. If a player has played well and is in real trouble because of bad luck rather then bad judgement then you can, and maybe should, ... cheat.
Your role as DM is to make sure the players have fun, dying in heroic circumstances can be fun; dying because the players all rolled 1s and the wolves all rolled 20s ... isn't. Cheating doesn't have to be as blatant as changing a dice roll; if you know the next hit can drop or kill a PC then have the monster do something else, drink a healing potion, cast a protective spell, engage someone else, flee etc.
Second, as one of the comments to your question asks, are there the expected number of characters in there (4). If there are fewer than this then you should scale back the number of monsters in each encounter.
Third, "foolish play = foolish death" is a perfectly reasonable equation. Player's who a) procrastinate and dither in the face of a clear and present danger or b) do something mind-buggeringly stupid do not deserve your sympathy or care.
An example of a) would be your characters wracked by indecision about what to do with the chained up wolves. If, after you have pointed out the howling and the straining on the chains and the groaning of the metal they still can't pull their finger out then "the wolf ate you" is a perfectly sensible conclusion.
An example of b): I played with a guy who reduced his PC and jumped into a statue's mouth to see what was inside - the answer was Green Slime - really, really stupid and simultaneously really, really funny. Funny deaths are often more memorable than heroic ones.
Sadly, the noble cleric Rumpelstiltskin was killed by a savage wolf. His companions grieved and buried him and toasted his life back at the inn.
Rumpelstiltskin's player needs a new character - fear not, he does not have to be Rumpelstiltskin's clone. The D&D basic rules cover basic character creation and are available free: