For 16 years I've bought Christmas and birthday gifts for my sister's children (first born 16, then 14, 11 and 9) without a thank you from anyone, not child not parent. They live in a different part of the country so I don't see regular. AIBU to say this is the first year they don't get a gift to see what happens?
Before you jump I wouldn't expect a baby to say thank you but I would like to think the parent might. Also I don't buy for thank yous but after 16 years it's got a bit annoying.