According to the current DLRP brochure (p49) "Kids Under 12 Stay, Play & Travel Free 6th January - 19th March 2008".
March might not be any warmer than November though.
Also there is the Get 1 day & l night free offer (p51) which according to the brochure can be combined with the Kids Go Free offers when dates coincide, so that might be worth considering.
The dates with free nights offer are:
4 days/3 nights for the price of 3 days/2 nights
9th November - 20th December 2007; 6th - 19th January 2008; 3rd - 6th February 2008; 7th - 12th March 2008
5 days/4 nights for the price of 4 days/3 nights or 6 days/5 nights for the price of 5 days/4nights
3rd - 7th October 2007; 9th November - 20th December 2007; 6th - 19th January 2008; 3rd - 6th February 2008; 7th - 12th March 2008