What are your thoughts on other people employing your nanny (or if you are a nanny, getting other work)?

Going against the grain here....I think as long as she is available to work for you within her contracted hours (i.e. she will drop any extra work if you need her) then it isn't really a problem. If you'd asked her to do a school run/sick care/holiday care and she couldn't due to working somewhere else then of course completely out of order.

If she's pregnant, going on maternity leave at some point, possibly worrying about money, someone asks her to do a a couple of hours ad hoc childcare during a time that you never use then I can see why she'd do it.

Whilst she didn't tell you about it, she's not exactly keeping it a secret by dropping off kids at the same school that your children go to.

If I were you, I wouldn't tell her I know and ask her to do a school drop off/few things during the day and see if she is available as I think that makes the difference.

She is massively taking the piss here.

I would also, incidentally, take issue with her taking additional work when it is impacting her ability to do the job I hired her for (i.e. too tired for my job because she started another at 7:00am).

Working a job for CIH whist she is being paid to do another one?

No way... not on my shift, lady.

I would remind her of her contractual hours, and remind her that she works for me (and no one else) in that time. That's what your contract says, right?

I would prbably give this reminder in the form of a verbal warning, as working for someone else on my time is pretty far over the line into outrageous behaviour. How could she not know this is not okay?

Well out of line. Your nanny should not be doing other work during the hours you have contracted them to work, on contracted days - so the 4 days per week.
The other days of the week are a different situation I feel though as you have not contracted them to work those days.

Another nanny here that has a contract that states that I cannot undertake paid work during my contacted hours without proir consent of my employer - in fact it has been in the contacts of my last 3 nanny positions and I presumed it was quite standard, check your contract as you may well have this clause and overlooked/forgotten about it.

Contract aside I think your nanny is out of line and should have spoken to you before doing any additional work.

When our nanny found herself with plenty of time off when ds started preschool, she did a few hours here and there for other people. But they always asked me before they asked her, she always checked with me, and it was always very clear to everyone that if I needed her (e.g. children sick) then we would take priority. I didn't mind in the least, and in fact one neighbour actually used to pay me a small hourly rate for the inconvenience, which turned it into more of a nanny share. But I'd be livid if I found out our nanny had been working for other people without telling my knowledge - presumably if you actually needed her, she wouldn't be available?

I might be OK with this if they had cleared it with me first (conditions would be that there really was nothing to be done in the mornings and they were willing to cancel the other jobs at short notice if I needed them), but without that, I'd be very annoyed. In my contracts I have a clause which says that nanny isn't allowed to take other work (paid or unpaid) whilst they are being paid by me, without my prior consent.

If you haven't asked her to do nursery duties while children are at school, then the very least she could do is to ensure she gets a good rest during the day, especially if she is pregnant!

I think it's incredibly dishonest of her to be taking paying work for the hours which you are already paying her on the 4 days a week.

I can't understand why you haven't asked her to do nursery duties in those hours that your children are at school. She could cook them meals as well, and maybe even some light housekeeping duties (emphasis on LIGHT).

On the 5th day, unless you are PAYING her for that option of using her then it's fair enough that she is taking some paid work.

I think overall you are being taken for a ride. You are certainly not utilising her in the way you should have been to get some decent value out of all of the money you are paying her.

I would be fuming.
Does your contract state she is employed during those hours for sole care of your children?
I would call her bluff and ask her to drop the kids off at school but I am a bit of a wimp. The sensible thing would be to discuss it with her and how she intends to fulfill her obligations to you.
If your children are sick then she must be available to have sole care of them.