I don't think Gamzee would be colleting them consciously but has definitely had all of them over the course of his life

as for the baby question...I thought at first this meant they'd also have the same skin and proportions as the baby humans (so no horns) and was going to say that troll/human fankids would be a bit different with the parents unable to tell what species their kid is until the horns grow in (or don't! lol); also I'd be curious how it would be handled in candy

but I guess you probably meant that they'd look like grey little babies with small horns? which would be really cute. I think there'd be a troll boss baby