School Funds

My husband and I have a savings account set up for our girls with the understanding that it will be used toward their schooling one day. We have not set up these funds in an education only fund, but more like a market sharing fund. When they are 18 they will be allowed to take this money but only if we sign off on it. After the age of 25 they can use it without our signature. My probate question is that if we should pass away before they turn of age, can we make it so an executor can only sign off on the money for the kids if they are going to use it for school?