The episode "Eddie's Brother" has a rather humorous moment where Herman is advised by Grandpa to show Lily some of Eddie's old baby stuff to get her to want to have another child. Herman can't find any of Eddie's baby clothes or toys, so he settles for his own baby belongings. He wonders if his old baby bonnet still fits. It's not long until he's sitting on the floor wearing the bonnet, shaking his oversized rattle, and babbling like an infant. Lily sees this and she gets the wrong idea.
Marilyn: What is it, Aunt Lily?
Lily: It took a hundred years, but it finally happened: Herman has gone through a second childhood!
In another episode, Herman is having trouble getting to bed, and the only thing that helps is a walk through the park. Lily doesn't want Herman to go, as there have been reports of a 'dangerous person' in the park at night. (Naturally, it's Herman) Grandpa at one point tells Herman, "What's the big deal? Lots of people have insomnia, and you don't see them losing sleep over it!"