My DDs (aged 2 and 4) still shower with their dad on occasion. They like to ambush him when he gets home from work and heads for the bathroom lol, and have started demanding that they be bathed at 4:30 so that when he gets home, they're already splashing around merrily and he just starts the shower running again without putting up a fight lol I figure they'll stop showering with him when they become uncomfortable with it - if we pushed for them to continue sharing showers after they express a dislike for it, I would consider *that* to be inappropriate, but while they're happy to do it I don't see an issue. DH tends to just keep his back turned to them so they don't point and laugh at his junk lol.