Kids fight and argue...it's going to happen. I did some horrible things to my younger brother growing up. Sometimes we get involved, sometimes we let them work it out amoungst themselves.
Today was one of those days:
Older Daughter: 'No, No, No...I win. I'm a Megalania(an extinct 20-foot monitor lizard for you and me), and you said you are a marsupial tiger. I weigh 500 pounds...you only weigh 300 pounds....you can't win.'
Younger Daughter: 'I don't want to be a marsupial tiger...I want to be a Mosasaurus(40+ foot marine reptile)...then I would win!
Older Daughter: 'That would only work if I went in the water!'
I am NOT getting in the middle of that one.