to think acknowledging gifts is only polite?

I have sent parcels to children/grandchildren, who live 100s of miles away, and have to assume that they arrived. No-one has acknowledged receipt (they should have come 10 days ago-I allowed plenty of time), nor have I had a thank-you. I brought them up to thank people IMMEDIATELY for gifts or favours. In fact, I haven't heard from my family at all over Christmas. A bit gutted.