I think my opinion may be slightly skewed, as last weekend, I ran a bath for 5 year old granddaughter, and she immediately shut the door to make sure 6 month old grandson couldn't get in. "Because he might fall in". He has been crawling a couple of weeks,not pulling himself to his feet yet. Let alone being able to vault into a headheight bath. Without anyone noticing.
If a 5 year old can see a problem between water and babies... I would have hoped parents could.
And lbh, this wasn't a spontaneous run and jump. They knew it was there.