If it's a double vanity I'd put tape down the middle. My parents did that for me and my sister. If someone's stuff ended up on the others side we cleaned both halves! We never strayed much into each other's space. We also used the layered plastic tubs for all our stuff on the bathroom counter and it was to be all put up when we left the bathroom or we had stuff taken away and more chores. I plan on doing something similar when my daughter gets older cause it worked for us.
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