My mil looked after my 2 dc's when they were small, although she lived near by so she didn't stay with us. The plus side was that even now, the dc's are close to her and she could have them even if they were ill. The down sides were that her looking after children style was not always the same as ours, and she would often announce she was going on holiday with not much notice.
In your situation my main concerns would be
1) She would be living with you 3 nights a week. Are you happy to have her sit with you in the evenings and would she eat with you? How would you feel if it was an au pair living with your?
2) What commitments does she have at home - DH, DP? How would they feel about her being away for half the week (and messing up every Sunday?)
3) 2 1/2 hours away isn't very close. You may end up paying more than nursery if you feel obliged to pay her petrol money/wear and tear on her car. Do you have back up if her car breaks down or if, like now, the snow is bad and she can't get there. What will you do when she goes on holiday?
It really is a great commitment taking on regular childcare. I would think very carefully about this before you even approach her.
What happens when she wants to apply for another job? Or even just when the sun- weds that she's spending at yours, clashes with some event at home? I think this is fraught with potential difficulties - not lease sharing your home for half the week. However much you get on with someone not many couples want that I would really think it through. I would suggest agreeing a trial period, but if you give up the nursery places will you be able to get them back if needed?
I'd say you need to talk it over very carefully with your DH and MIL. Apart from the thing of having her there in the evenings (would be a big no-no for me), as you say, you need to be clear about how you expect her to look after your kids, eg how to use discipline, what to feed them, rules on TV, how hands-on/hands-off to be on trips out, etc. etc. You'd also want to be certain that the arrangement would stick, that she wouldn't get fed-up after a few weeks, by which point you'd have passed up the nursery places. What about the impact on your FIL? Might he get fed-up with it, too, and insist that it come to an end?
I'm due to return to work in a cople of months (part time mon-weds) DS will be just 3 and DD will be 11 months. DS goes to nursery 2 days a week and this will bump up to 3 days and DD will start at the same nursery 3 days a week too.
Well that was the plan but we are now considering a radical alternative! MIL is looking likely to be made redundant with no other viable job options. We had the thought that she could come down to stay with us (they are a 2.5 hour drive away) sun night to weds afternoon and look afterthe kids. We would pay her something like what we save in nursery fees which would be a help to DHs parents financially and the main benefit for us would be we wouldn't have to put Dd in nursery when I go back to work - despite the nursery nearby being outstanding ofsted and well regarded locally, we aren't over impressed and DS doesn't seem particularly happy there. We'd prob try to get DS into a preschool but for less hours than he would otherwise do at nursery.
Is anyone else in such an arrangement and can comment on how it works for you? Is it a real strain not having time to yourselves with DP in the evenings? That's my main concern. Also is it awkward or difficult to get your mums / MIL to look after your kids as you want her to? Any other negatives I haven't thought of? I have to say I'm cautiously keen as I can foresee lots of other advantages like being able to have the odd night out and not having to miss work if the kids are unwell!