We use hand me down bikes (3 kids, bikes of every size from the tiniest puky balance bike to adult size and everything in between in the garage - 7 year old has never had a new one, and won't until he needs an adult size one).
We don't give the hand me downs as presents though, they're just there to move up to.
Additionally we bought the older children cheaper second hand bikes if they outgrew their current one in a growth spurt without it being a present.
We've only given new bikes as actual Christmas and birthday presents a few times. I think the first balance bike was bought brand new for Dc1's 2nd birthday, and both older kids had brand new bikes for their birthdays at 10 and 8 when they were the same height so no hand me downs.
After cycling proficiency test at the end of primary we buy each child a really good adult size bike which we expect to last them for good (dds definitely will although if DS passes 6 ft he may look a little silly on his... Still it'll last several years!)
I wouldn't give a hand me down as a present but absolutely would hand it down!
Accessories are definitely presents if bought for the child personally - baskets, bells, lights, speedometers/ mile counters, drinks bottle with rack, those silly fake exhausts, flame stickers to decorate a hand me down