Why is it that large families can go on holiday for cheaper than me and my son?

i'm a single parent of one child, so i would expect to pay less for a holiday than a family of 4 or more. How wrong can I be? All the holiday and budget deals are for families of 3, 4 or more, so they can have a entire week at a UK holiday park for �99, while I have to pay �429 for the same holiday, or if I want to go to a holiday village in Spain I can't get the kids go free deal or the budget holidays, so a family pay �499 for the entire holiday, while I pay �749 per person!!!! At this rate I will never be able to go on holiday. What's worse is I keep getting sent all the family offers through my door just to rub it in!