My fiance and her two daughters (8 years old and 4 years old) live with me and my two sons (7 years old and 10 years old). 6 people is quite a houseful :) The girls father sees them once a week for a couple of hours. When they are with him, they get everything they want and when they get home I usually hear "That's not fair" from my two boys. I am not able to buy the boys whatever they want, whenever they want it, not that I would if I could afford it.
Just last week the girls wanted to get American Girl dolls. So they call their father up and get him to order them some online. They know that if they want something, they only have to ask their father.
How do I explain to my sons that there is nothing I can do about the girls father buying them things all the time? It's not that I want to "compete" with him, but he makes life for me pretty difficult at home each time he buys the girls something.