I was thinking about that when I was dropping my 6 year old off at some hobbies earlier - it's pretty much expected to have learned how to ride a bicycle before starting school, and it massively expands the area you can go to by yourself. When she went to school by bicycle she can easily make a detour via a shop to spend some pocket money before coming home, while by foot that'd be rather time consuming.
Quite a lot of friends from outside of Europe either can't ride a bicycle, or were learning it as adult after moving here, though.
edit: the high number of replies mentioning "swimming" made me realize that I had that filed as a basic skill pretty much everybody has - probably due to swimming lessons being a mandatory part of school education here.
Cutlery.
Growing up everyone around me could use a knife and fork, whereas chopsticks were something most people couldn't use or only used badly. It never occurred to me that the opposite might be true until I shared a meal with some co-workers from mainland China and saw how clumsily they used our utensils.
It wasn't until that point that I appreciated the amount of dexterity and finesse that goes into using cutlery well, and that I took it for granted because it's something learned in childhood.
Did you know the details on how to eat with knife and fork differ across different countries as well?
Maybe I shouldn't be saying this since it's cultural, but I feel like if it is possible to use cutlery wrong, then I think the American style is definitely one of the wrong ways.
Never before have a I hoped that a Wikipedia article is part of an elaborate joke.