As you take a client through you say "oh sorry, the children can't stay here unattended" then see how much they enjoy their facial or Brazilian with kids there. They will never bring them again.
A simple sign saying
"For insurance purposes, children cannot be left unattended" is enough.
If you have regulars who book for a Brazilian then bring 3 children with them, you can call them and say "just to let you know, for insurance purposes, we now have a policy that children can't be left unattended". They then have the option to change or cancel their booking. You can even hint that something happened.
I was waxing a clients lip and she left her baby in a car seat and her toddler on their own in my reception. I had the door open and was the only therapist in. I heard a noise and looked out. The toddler was skidding the car seat all over my brand new floor. I just ran out and said "OI THAT'S ENOUGH. You have to sit here quietly" which the terrified child did. She's not been back. Shame
On a Tuesday I'm on my own in the salon and tell clients that they can bring babies in if they want to. I'm a breastfeeding counsellor as well so sit doing a pedi advising on their latch lol. As the child gets older, the parent realises that the salon is no place for a child. I make it clear
Vic x