This is a strange one, but at roughly what age did your children start actively asking for presents for Christmas, birthday etc? DS is 3.7 and would never ask for something in that way. If we're in a shop and he sees a toy he might say can we buy this, but he knows the answer is no so often just asks to look at the toys.
We were at a friend's house yesterday and her DS who is only 3 months older was saying I want this or that for my birthday. DS would never do that; I don't know if it's something I should expect him to "know" to do (he tends to watch pre recorded tv so not many ads and I don't really talk about Christmas/birthday etc). I did ask him what he wanted today and he said a fire engine (he has about 5 so that's a no!) but he would never see a toy, make the connection and ask off his own back, if that makes sense.
Thanks!