If you are going to be in Gran Canaria for Christmas or New Year (or both!) you might like to visit Holiday World which is in Maspalomas. On Christmas day they have activities for kids from 5pm until 11pm, including a Santa grotto, face painting, clowns and a show. There are fairground rides there too.
On New Year’s Eve there is a party from late afternoon until 4am, including food, drink, live music and more. The price of the New Year’s Eve party is 30 euros a head but the Christmas one is free to enter. Holiday World is near the Faro 2 shopping centre in Maspalomas so you might like to have Christmas dinner in one of the restaurants there and then head over to Holiday World with the kids.
You can find out more about Holiday World here: http://holidayworld-maspalomas.com/