It depends on how independent your 4 year old is.
My ex husband would bring my daughter to the handicap toilet and he'd start guard outside while she goes in. Afterwards he'd ask the usual "Have you wash your hands" and that's it. Worse case scenario, he brings my daughter into the men's toilet while closing her eyes and start guard outside the cubicle. He never goes into the cubicle with her at all.
Read more