I have been advised by a Thomson rep at the call center (0870 165 0079) that if you are booking children on your holiday it is sometimes cheaper to book them as adults not children for the accomodation, therefore you don't get charged any under occupancy charges (i.e. children are classed as 0.5 people; therefore if you have two adults and two children in a 4 bed apartment, you will get charged under occupancy for 1 person!!).
By classing my two children as adults for our holiday next year I have just saved us £322 (compared to the online quote which was the lowest available) on a two week break!!!
Definately worth a try!