Any gift is welcome and don't give many ideas to make it easy. Anything that has a little thought behind it is what matters.
I think it is important for children to believe in father Christmas for as long as possible. It is a magical time of year for them and keeping a belief going for them is important.
I used to be Santa taking in my kids Christmas stockings every year and did it up to the age of 20. Obviously they knew by then but it was the extra gifts they used to look forward to each year.
In our house you open gifts on Christmas day but you will get an array of gifts appear at the base of your bed overnight normally in a pillow case. The gifts range from expensive aftershaves and perfume to computer games and chocolates. Thankfully I have stopped that these days as it would cost a lot more now they are older.
I did not expect anything in the first place :) But to answer the second part of the question...I think that most children nowadays now quite well that there is no such thing as Santa or Father Christmas and just play along because their parents are so eager to make this all up. You might impress the youngest among them but they will figure out very quick what this is all about. I for myself was horrified about Santa when I was a kid. My parents went to a Christmas market with me in order to meet Santa and all there was was an old grumpy looking dude in a poorly costume, smelling of booze. As a result I was running away with light speed screaming. From that point the whole Santa thing was done.