My grandchildren get through several pairs of school shoes a term but we are walking a mile to school and back each day and modern shoes have such flimsy soles. Sometimes I will buy them, sometimes my daughter will (she is a single parent, son in law is supposed to pay £50 per week towards the costs of raising 3 children but that goes nowhere with three sets of school uniform, shoes, boots for Winter, Winter coats, bags, lunch boxes, gym uniform, wellingtons and outdoor clothes for Forest School etc etc.). If you can afford to pay for the shoes then offer to do so, if you cannot or do not want to make a commitment that will be ongoing you should be honest and say so clearly so there is no misunderstanding. Finding the money for an unexpected school item you thought was already covered might be hard for them to do unless you give them enough warning.