DD and DS1 bathe together and they have been left alone for a few mins at a time since DS1 was about 2, so DD would have been 3-3 1/2. I would maybe clear the table, or get their clothes. I will now leave them for about 10ish mins while I do the kitchen or dress DS2 from his bath. I can always hear them nattering away together and make them call to me if they're too quiet. They're now nearly 3 and 4.