I have always been given goodbye gifts in the past (from work, from school friends, even if just changing departments in the workplace etc) so to me, goodbye gifts aren't uncommon. I give the families goodbye gifts and most give me one as well. It's a small gesture to say that they will be missed and I've enjoyed knowing them/caring for child. In some cases, I didn't get a chance to buy a gift (either forget or not enough time) but they always get a card with a heartfelt message written by me.
I've only had the one leave for mat leave but even when friends or families have a new baby, I have always given the older sibling a small gift as well...sort of like a "congrats, your an older sibling now". If there are multiple older siblings already, I give a gift they can all enjoy. If I attend a wedding and there are children blending into one family, I give them a gift too, as it's also a special day for them.
I understand what you're saying sparks and self entitlement is one of my biggest pet peeves.....but I'm a gift giver!!! Lol. However, if I felt the child or family EXPECTED a gift from me, than you bet I wouldn't give one!