My kids are 5 and 2.5.
I'm a single parent working full time and living in a small 2 bedroom flat.
When my kids go in the bath I use this time to tidy up after dinner, make packed lunches and prepare for bedtime. My flat is tiny so I am never far away from them. I listen the entire time and check on them every few minutes, I'm very tuned into what they are doing which is usually playing calmly and happily together. There are times when one gets upset or they squabble and when this happens I sit in there with them or get them out, but most of the time they're fine.
Am I unreasonable for doing this?
YANBU - using this time to get on with chores is fine, you check on them regularly.
YABU - they are too young to be left alone in the bath regardless of how close by you are.