Do Canadian children need a passport when entering the park from Canada as the adults do?

NO! Do NOT listen to these people! They DON’T! If they don’t have a passport a birth certificate will do as well, I went with my birth certificate and there was no problem.

Not sure I'll ask this week

Yes, have all passports of coming into the U.S.side from Canada. The border guards are checking as you leave the park.

Yes

Whatever you needed to cross precovid I the same now. So assuming Passport or nexus.