My eldest was over 4 before i left him alone. I did sometimes run to get the phone or towels ect but i would call out to him.. My second son was around 2 as the boys bathed together and I was just pottering around fixing up their rooms for the night which are on either side of the bthroom anyways..

now all 3 or just my 2 youngest boys bath together. We can hear them at al times..