A year ago I asked DB to make sure that his kids systematically send a thank you (by email is fine), as I live on the other side of the world and it's my only form of communication with them. I have two nieces aged 11 and 9 and a nephew aged 7, and in our own family DB and I were always made to send thank yous.
Since then, the 9-year-old sent me a one-line email literally saying 'thank you for my present' (no mention even of what it was), the 7-year-old sent a lovely email, and I'm still waiting to hear from the 11-year-old, who I sent a book voucher for her birthday in June. I mentioned it to DB a couple of months ago but he said they hadn't had time to go to the bookshop (!).
I feel I'm not prepared to keep spending my time and money buying presents when I don't even get an acknowledgement. Would it be unreasonable to write to my brother at some point and say that if I haven't heard by April or so then I'll just be sending a card for her next birthday?