Playhouse by Robert Munsch.

Rene's parents are as nice as can be. When Rene asks her father to build her a playhouse, her father says "good idea," and builds her one. When Rene tells her mother that her playhouse needs a play barn, Rene gets that too! But before long Rene wants a play cow, a play tractor ― even a play mommy and play daddy. When her mother refuses to build her a play mommy and a play daddy she decides to make her own. But when she finds that her parents have replaced her with a play Rene, she quickly realizes that REAL families are the best of all.