Do you have written contract which spell out agreement made? If you believed they would be more FT then are, a parent would point out misunderstanding before signing.

Do you just charge for days they come? Most carer charge for days they enrolled and fee due if they off sick, on vacation or having a day with parent/grandparent.

We have lot of rotating shift client in this area. Because day they work changes week to week, they need place reserved for child on each day. But they have pay for full time place even if not using every day otherwise carer would just turn away and wait for a client who need every day. It only way carer can control own income.

If I you, I would be seeking replacement. If you have contract, once found replacement client who need each day, and once they sign contract too, then make start date so you can give notice to current client and the finish immediately before new client begin. If you not have contract, then you can just terminate when new person want start.

It sound like your 2 current children will not need FT ever. You could alway message both and state this not agreement you had and you require FT payment/attendance but if they not work FT then they unlikely to want change current situation now they have this arrangement with you. And there is risk they just pull their child before you have new client line up.