I'm no use I'm afraid as DS has 6 kids in his area and one key worker as that's the ratio for 2-3 yr olds here in Ireland - 1:6. Tbh it seems to be fine.
There are floating workers to help out but there are definitely a few minutes here and there where she's changing a nappy in the adjoining toilet and the kids are technically unobserved.
But then we don't have a handover as such. They do write things down but at pick up she just says "He ate well, he slept/didn't sleep, he had a couple of stroppy moments but nothing major". So it takes literally 30 seconds and she doesn't step away from the kids whilst she's saying it.
Now in fairness we are pretty hands off and as long as he's obviously happy we're happy. It's largely a personality thing too - we absolutely adore his key worker and genuinely believe she'd tell us anything important, whereas we might not trust someone else.
For example she starts at 9 so before that the woman from the Waddlers does the 2-3 room with her little ones mingling amongst them. We aren't so fond of her. She was nice with the tinies but seems not to know how to talk to Toddlers and comes across as bossy and hectoring which is guaranteed to cause defiance. Whereas our Keyworker is gentle and does a lot of clever fun distraction with toys to get them to do what she wants and it really works.
So it comes down to trust I guess. I wouldn't trust Waddlers Woman half as much to report everything. We actually try not to arrive before 9 as we are so sick of her snotty tone. "Dad, take his coat off please!" which just makes DS shout NO! and cling on to his coat like a vice. Not helpful!