No, but be prepared to point out what you're offering - flexibility over 2-5 days a week, first aid training, childcare experience and a diploma in CLD. Have you asked around about charges? spoken to your tutors about going rates? over and above child-minding?
Are you having to use a car to collect the children? Expenses to get there and back and the time it takes you to get to collect them? If you only did the 2 days, you'd be earning £2400 pa - the full five days £6000 or so if it's just term time. No tax but NIC.
I'd also research nanny contracts so you know the pitfalls. And have a serious talk with your future employer.
There are very few nannies in North Wales so very hard to know what would be reasonable.
I would look at what other childcare options cost in the area, see if you can find something to compare with, then add a bit more to it as you would be providing 1:2 care ratio and other providers may not be doing so.
Agreeing gross is a fantastic idea, as then the parents can calculate what it will cost them over a year.
Keep in mind that you get paid holiday. For a term-time only worker, this is usually done as 12.07% of working time, with the constraint that you cannot take holiday during term-time. The holiday is taken at the end of each term, or spread out over monthly payments.