E.M.
My 17 months old did this for the first time the other day. I didn't punish her or even tell her it was bad. I don't think she would understand. Also, I don't want her to associate going to the bathroom as something bad. Actually, a few days later she was a bit constipated and struggling to go #2. I put her in the tub and 5 min later, she had gone in the tub. So, I actually used it to my advantage (and hers too). She felt much better afterwards and was in a much better mood!!