'Have you been good this year.'
'What do you want for Christmas?'
'Will you leave carrot out for my reindeer/mince pie/drink etc on a Christmas Eve?'
Keep in mind that three year olds have a v limited idea of the whole notion of Christmas.
(Ps - tell him not to do what one Father Christmas did to me, I had thing 1 and thing 2 on each knee and Santa leant forward and began stroking one of their arms but he was actually stroking mine, not good!)