they advised the contract as standard would meet the legal requirements, stating that bank holidays would be included within holiday entitlement not in addition. But is that kind of behaviour frowned on?
No, as a nanny who likes working part-time full day jobs this is standard and is to be expected. These days I don't even expect to have a bank holiday off as many parents do need to still work those days.
Working 2 days per week your nanny is entitled to a minimum of 11.2 days of annual leave. Could you offer more, such as 12, 13, 14?
Bank holidays occurring on a Monday will vary a little year to year.
Assuming you are in England, then in 2021 it is 5 on a Monday, in 2022 there are 6 bank holiday Mondays, 2023 there are 6. In those 3 years there are no bank holidays on a Thursday - be aware that it does happen sometimes.
Feels very mean - but on the other hand - it starts becoming very expensive to hire someone PT (on a Monday) if I don't include bank holidays within the holiday entitlement. Would you state this is what you are going to do as part of the offer to the nanny? Just trying to work out how people hire a PT nanny if that also includes a Monday.
So if you agreed 12 days annual leave, then that still leaves 6 days, of which you may choose 3 and they choose 3, or you choose 4 and they choose 2. You decide how many you choose... you legally can choose all but I would not do that.
The nanny has asked if there is any chance we could move her Friday day to another day.
So you are being nice in accommodating that and by doing so it means that if Monday is the day agreed then it will mean a lot of annual leave is used by bank holiday Monday's. That's the way it is when an employer does not need their employee to work on a bank holiday.
Would you state this is what you are going to do as part of the offer to the nanny?
Yes absolutely. I would even try to provide a calendar of all the pre-selected annual leave days for the next year or two so there is no misunderstanding that those days HAVE to be taken off as annual leave, but keep other dates variable so you and they can have some choice. Do look at weeks like Christmas and determine if non-bank holidays then will also be determined as annual leave days right from the start.