sick of parents treating me like a charity!!!

Don't put up with that!
I agree with the Provincial lady.
Whether they are well off not is not really the point imo, they have a contract with you, they must stick to it.
Do not feel embarrassed about challenging them, it's them who should feel embarrassed.

Write a letter to all your parents, saying that up until now you have not applied the late payment charge but that from next month, you will be forced to do so due to rising bank charges, interest rates etc. Say that you are willing to discuss terms in cases of difficulty. Then enforce it. They have got used to the idea that they can do this, so they don't make paying you a priority. Bet they pay their mortgage on time though!

I have a late payment fee in my contracts, but I'm generally too nice to charge it, unless parents are really taking the mickey. Most of my parents are fine. I send out invoices much earlier these days (ie 15th Jan, for payment on 1st Feb - used to be 25th). This is supposed to mean that voucher payments will arrive on time, but they don't. It's the voucher payments I hate and if they didn't save parents so much money, I would refuse to take them.

My contracts specify - no payment, no childcare - so if someone was really taking the mick I would probably have to turn them away until I receive payment.

When you say you expect payments on the 30th, is that in advance for the following month, or in arrears for last month? I always charge in advance, because I have heard too many stories about people just disappearing and not paying.

my contract says that fees need to be paid in advance by the 1st of the month otherwise there is a 20% late fee added on

I don't know if this is normal practice for childminders but certainly normal for nursery/after school club. We pay the bill in advance and get a late payment charge if not paid for by the end of the first week of the month in question! e.g. if not paid bill for Feb by Friday 4th feb would get a later payment charge the next month.

If not in your t&c's at the moment then can you add as a new condition - would have to give notice I imagine and say with effect from ddmmyy any late payments will be subject to an additional late payment charge of £xx or x %?

oh dear

what terms do your contract state?

don't speculate on the state of your parents' finances, although they have well paid jobs they may have outgoings you don't know about ; however persistent late payment of their childcare fees is unacceptable and I understand your frustration