I took my boys in the bathroom with me until they were about 8. At 8, they didn't want to go into the ladies bathroom because they were embarrassed. (they were really tall for their age) I would make them go in together into the men's restroom.
A friend of mine said she would make sure no one was in the men's restroom and let her boys go in and if a man came up while her boys were in the bathroom. she would ask them to wait just a minute for her boys to come out and she said no one ever minded, or at least acted like they didn't.