Did it for the first time last year but think I went a bit overboard, not in cost terms but in the amount of stuff I put in.
iirc it was Christmas Eve pyjamas that they've always had anyway ( and their grandad always brings new pj's xmas eve too which they wear Christmas night )
Various forms of chocolate/sweets, a Santa key for dd, Christmas craft sets, a DVD each, Christmas slipper socks, various other bits and bobs.
To be honest they were only interested in the chocolate and dd who was 5 nearly 6 wanted to get the craft stuff out at bedtime!
This year I'm not going to bother, new pj's, DVD ( always done this ) and chocolates and that's it.
They will be getting far too much on Christmas morning anyway.
I have decided to buy some craft for dd to do during Christmas Eve afternoon to keep her entertained with dp whilst I do my big Christmas Eve clean.
Ds is nearly 15 and goes to the cinema every Christmas Eve and for a meal so he's not bothered.