If you are going in January, why not consider using the Eurostar. If you book through somewhere like Leisure Direction or Clippers Quay, you get the child place free for the hotel and any character breakfasts, and the eurostar for free too. I see you are in the West Mids, so could travel from Brum to Waterloo, or even drive to Ashford to pick it up.
I find that when booking packages through these companies that they get such good deals that the travel part of the package cost is pretty much zero. For example we did 3 nights at the Santa Fe last Jan with 2 adults and 3 kids (1 baby) including travel and all passes for a shade under £300. This year we are doing 5 days at the Sequoia Lodge including character breakfasts nearly every day for well (and I mean WELL) under £1000.
Clippers Quay Travel is on 0845 367 4000
Leisure Direction on 0871 423 8955
Definately give one or both a call!! Even if you really want to fly they can probably price beat.
Amanda (I have nothing to do with either of these companies by the way, just find them very good value!!)