I can remember being three years old and being given the exact same tin of jelly beans by one grandparent that I'd been given by the other on the other side. I very excitedly yelled that I'd got two cans of jelly beans now, and got embarrassedly shushed by my parents and told we don't say things like that, we just say thank you very much. I was very confused because I thought it was brilliant. I really liked those tins of jelly beans. . .
At 8, the kid has had time to learn the basics of please and thank you. Difficult if he's not being taught or having them modelled to him though. If he does the same thing this year, has to be prompted to say thank you, and puts an ungracious little rider on the end of it, I'd be tempted to do him a favour and very quietly explain to him that all it is necessary to say when no one is obligated to give a person a gift, and if someone is lucky enough to receive one, what is required is to say a polite and genuine, 'thank you very much' - no more, no less. Because otherwise people might find that they start getting no gifts at all. . .
I've got nieces and nephews in their twenties now. In all the years I have bought them gifts, I haven't had one of them say 'thank you'. Their parents may have, when they were younger, on their behalf. This year I decided that I'm not buying gifts for them any longer. I'm sure they won't notice, and that's okay. (It's equally okay if they do notice, as far as I'm concerned, lol).
We all get and give a bit too much these days, I reckon. It's lost a lot of the value, meaning, excitment and genuine pleasure at receiving a gift even if it wasn't exactly what we would have liked to have got.