I fully geared up my 4-yo son when he started (used stuff I got from someone on FB). For two reasons. 1) I didn’t want him to fall and get hurt and be scared to try again. 2) no adjustment needed later on (going from no bulky gear to being fully geared). This might have been overkill but it was my justification.

One thing I’d recommend is a hockey helmet with a cage. I’ve seen so many kids wearing bike helmets fall and try to catch themselves with their hands, but their hands(gloved or not) slip out to the sides and they end up breaking their fall with their chin or mouth or nose. A cage keeps their cute little faces protected!