Ive never put a stop to it, rather Ive let my children let me know when they didnt want to shower/bath with me. I dont think something is 'dirty' or inappropriate unless someone makes you feel it KWIM...
All of my kids still come & chat to me while I'm in the shower, including my 13yo son & 15yo daughter.. ok, so they don't get in with me, but I don't think you have to worry about scarring them, if you leave it up to them as to what they are comfortable with you're pretty safe.
They are all very modest when it's them showering / bathing, but me...meh, I'm a mum ... they seem to think I'm immune, privacy? What privacy?

FWIW I think we stopped showering / bathing together around 4 -6 years...soemthing like that. They will definitely let you know