I agree, most ballets are family friendly. If they weren’t, it’d be hard to make some ticket sales!
Just be aware, some ballets are very long… Swan lake being one of them. Depending on the version, and the amount of acts and intermissions. Sleeping Beauty is actually typically long too. It’s almost always 3 acts, so that means two intermissions.
If your kids have long attention spans, this is great! If they don’t you may want to wait a bit. The nutcracker is great because most versions move very quickly, especially in Act 2 with all the different divertissements.