When Timmy wished for all the babies to be adults, the wording of the wish should have turned Poof into an adult too. However since Cosmo was the one who made the wish come true, he may have done the wish on everyone but Poof due to him often being unintelligent.
When Timmy and his parents were making brownies, Dad is rolling out dough on a cutting board. Brownies are made of batter, not dough.
When Timmy's Mom and Dad barged into his room, they produced a red wagon out of nowhere.
When the Tooth Fairy (as a baby) was in the brownie pan about to be cooked by Timmy`s Mom, the oven spits out fire. This is impossible, because the oven can`t reach that temperature.
When the babies are watching Lookee Lookee's Lunchbox, we see that Cupid and Juandissimo are next to each other. However, when Timmy takes out the TV's screen (and we see the babies from the back), Cupid has disappeared and the Tooth Fairy is next to Juandissimo. Cupid is back in the next shot.
Juandissimo was hypnotized with his reflection and cried because he was watching Lookee Lookee's Lunchbox, but after Timmy gives him the mirror, he was hypnotized watching Lookee Lookee's Lunchbox.
Juandissimo's mirror disappears after Timmy gives it to him.
When Timmy hits Cosmo with the second arrow, it is huge, but when Cosmo comes into Timmy's room, it becomes normal size.
It is unknown why Cupid was turned round after Timmy made his wish as he is not a fairy. He is actually a Roman God.