Should parents continue to support all expenses after their child have on-campus job?

We are continuing to pay all expenses for both kids except for discretionary spending up to the end of their first year of university. After first year we require that they also pay for their living expenses while at school (housing/utilities/food/incidentals) out of summer earnings while we continue to pay for all school related costs (tuition/fees/books) and other expenses (clothing/phone/car insurance etc.). Even though in addition to working summers for their first 2 years of university, both will also have paid internships of between 12-16 months following the 3rd year of their programs, until such time as they complete their undergraduate educations we will continue to cover the majority of their costs as we still consider them to be dependents and we can afford to do so. Having them pay for some of their costs is more an educational experience for them than a financial necessity for us.