Amanda, I've been in a similar-ish situation to you, where a complete wanker ex sent me a christmas card, several months on, as if nothing had happened.
The reason why they do this ? ......
..... 'cos they are full of guilt and therefore by doing something "normal" like sending a card, they can pretend to themselves that as they're being "friendly", they've actually done nothing wrong.
Which, of course, is absolute bollocks (excuse my French!)
To send it to a child - thus potentially running the risk of upsetting them, and the possibility of "what happened to so and so" type questions, proves, as if any more proof were needed, what a complete twat he is.
The best thing to do is utterly ignore it. Certainly no calls or texts, even if they are along the lines of "how dare you send me ......."
Don't give the little toerag the satisfaction of believing you actually care a jot about him in any respect - not that you do - but I mean care enough to respond at all to any of his actions.
Despite all your hopes for Xmas this year, you do realise you're better off without him don't you. Take care.