Normally, toddlers or babies can't take a bath or wash their hands by themselves. That is their parents who do these for them.
In the dictionary
have something done (used with a past participle) to cause something to be done for you by somebody else
You've had your hair cut!
We're having our car repaired.
So, am I wrong when I say these to my 2 year-old son
Hey Jonny, let's go wash your hands, let's go take a bath, let's go wash your ass, etc. (Note: I will do these for him, he can't do them by himself.)
What do native people say? Do they say like these?:
let's go have your hands washed
let's go have you taken a bath or let's go have you bathed
let's go have your ass washed