i think, these sort of things are way to difficult and individual
perhaps the best thing if there is such a thing in these cases
would be to check with somebody who makes markers
and then find out what ideas they can come up with, given a couple of unique items / things that were dear to the infant/child
it's so very personal for the parents, that i would think it's a custom job every time
the identity of a grown up, is usually well defined and well known , so the style is easier to pick, but an infant, everything is possible, some like is ultra sober, with just a moving line of poetry engraved, some engrave a picture, or a religious thing...
my aunt lost 2 kids at young age, both graves were abstract modern
maybe there are little examples , because it is such a difficult situation
parents are grief stricken, and will be very sensitive and protective for long times after
and would not be accessible to have their custom made grave put up on display
sorry to hear about your loss