Why can't we have another brother?

I repeat I am not pregnant!!  Now with that said here is the conversation Martin and Roxie are having in the back yard.
Martin: Roxie we are going to have a brother because we need to have three boys and three girls.
Roxie: We are NOT (yelling) having a brother or sister!  I like our family without any more brothers.
Martin: No we HAVE to have at lest one more Brother.  Its not fair! We have a dad and me but you have a sister and a mom and you! We need a brother
Roxie: I don't want any more brothers or sisters!  NO (Yelling)! I will be so angry if we have another brother.  I like you Martin
Martin: I like you Roxie but I need a brother to play with.
Roxie: I want to play with you.
Martin: No Roxie I need a brother to play brother things.
Roxie: I can play brother things.  Martin do you want to play princesses?
Martin: Mom see we need a brother.

Both kids came into the house upset about Martin not playing princesses and wanting a brother.
Me: Martin the only way a brother might come into this house is if everyone is nice, kind and we do not fight with our sisters.  Roxie it isn't up to you if another baby comes into this house. Martin one more thing if another baby ever comes into this house it can be a boy or girl. They both walked outside saying "Mom isn't being fair!"
To be honest every day between 5-6pm is the reason there isn't another baby.  Birth Control hour!! The kids for some reason go crazy and fight non stop with each other.  They spend more time in their rooms between 5-6 than any other time of the day.

Sorry I do not have new pictures of the kids!