Mommy needs to potty
Reliably? Maybe when they are 4 or so? For sure once they are in pre-school/school and the boys and girls have separate bathrooms, and they start noticing that they don't see other people using the toilet. When my kids started to get the that stage, they build a 'change room' between 2 dressers in their room. After they had their bath together, where both of them were naked and didn't pay any mind to it, they would go to get their jams on. They would take turns in the change room, and while they were changing, they were screaming at me that the other one was peeking, make them stop!!
My son is 3, going on 4, and not only do I get an audience from him and his little sister nearly every time I use the restroom, but there are category 5 meltdowns if, God forbid, I accidentally flush the toilet myself without letting him do it. He wasn't interested in that for the longest time, but now that the toddler wants to, it's become a life goal of his to flush at every opportunity.
No matter what my 3 y/o son is doing, he will always follow me to the bathroom. Sometimes he will sit next to me and ask to hold my hand...I think that's so cute. Other times he will comment on the contents of my toileting activities....truly....who else would be so interested in my poop?