Definately normal. It's not like they were trying to have sex. My friends and I all used to shower and bathe together as kids, and we are all straight. Its probably just about fitting in, nothing more. Now when he is 20, you might have something to worry about.
Trust me, in this economy, people are not gonna pay for some kid to walk their dog for them. And if they are, they are probably perverts or something. Be careful. Don't think it's a good idea.