Your school district should have a policy regarding student transportation which may provide guidance regarding changing bus stops. Your school district should provide this to you upon request. The Pennsylvania Department of Education has additional guidance regarding student transporation on its website, www.education.state.pa.us.
Provided the children's change in physical custody to your son's home does not place them in a different school district or within in different school boundaries within the same school district, the school district should transport the children to/from your son's home (their registered address) to their school.
Sign up to receive a 3-part series of useful information and advice about child custody law.