Unlike the prior sitcoms Seinfeld uses the new children style of representing by using growth people playing like a kids. Many sitcoms after that started using the same idea.

The post-Seinfeld sitcom that also uses the grown people behaving like a children is the Family guy where Peter Griffin ( father) is the one who acts more like a kid. And when he meets with his friends Quagmire, Cleveland and Joe they have the typical children's conversation. On the other hand, Bryan, Stewie and Louis griffin that in my opinion have the grown people behavior even though Stwie is a little baby with British accent that wants to kill his mother.