Male Cleaning Female....?

First off let me tell you how much I enjoy this site! I have come on with odd questions and always get the info I need!

My question now is....

Is it normal for my 8 week old male kitten to clean the female kitten's bottom? Like mom used to do when they were young. He doesn't do it to the other male kitten but does try to 'clean' mom too. I could understand if they were in heat or something, but they aren't. Well, at least the baby isn't!

I think it is perfectly normal and often continues into adulthood. My two boys, both neutered of course, often groom each other and the girls. It becomes a real beauty parlour at times!