I've been in the process of sewing some clothes for a newborn coming in the next few months. In looking at designs for sleep gowns, it seems like they almost universally go over a child's head, even though many people recommend avoiding that the first month or two of a child's life and look for something with a zipper or a side snap style - a preference these first-time parents I'm sewing for share. Is there some reason I'm missing not to put a zipper or buttons down the front of a sleep gown? Pros versus cons for zipper versus buttons?
For a newborn, hands down zippers are the ideal option over snaps, and snaps would be better than anything pull-over. There's nothing more confounding in the middle of a sleep deprived night than snaps. Trying to match them up in the dark while baby wriggles and your eyes are crossed from exhaustion is hell.
The only disadvantage to a zipper is the slight chance of zipping up baby's leg (or some other body part) in it. However if the sleep sack/gown is roomy enough (as it should be) this is less likely to happen than with, say, a "sleeper" (the one piece pajamas with feet) that are a little more close fitting.
The reason commercial nightgowns don't do this is because of consumer product safety commission regulations requiring children's nightclothes to be either self extinguishing or close fitting to avoid burns. A zippered nightgown leaves the manufacturer open to lawsuit if the parents leave it unzipped and then drop a cigarette butt on it when they fall asleep and the child ends up burned.
That shouldn't be an issue when making a personal gift, especially if the parents don't smoke, so you're free to use or create a design with a zipper.