Hi, I'm sorry to hear your daughter is struggling with finding a reliable, safe way to transport her children to/from school.
Here are a few potential solutions you and she might consider...
1.) Talk to the school or school district to find out if they have school buses available. If located in the United States, you can use SchoolFinder to research the school or district's phone number. http://www.education.com/schoolfinder/
2.) Arrange a ride for the children with another parent at the school -- perhaps one of their neighbors who also has children at the same school. Your daughter could also offer to pitch in for the gas expense, or offer to babysit in trade for the ride. If your daughter doesn't have relationships with her neighbors, she could also try contacting the school's PTA to be connected with other parents at the school.
3.) Hire a helper (nanny, housecleaner, tutor, etc.) with a driver's license to shuttle the kids to and from school in the morning and afternoon.
4.) Arrange with a child transport company to either transport the kids to school. In our area (in Northern California), there are a handful of nonprofits that do this for a relatively small fee. Try doing an online search for "child/school transport" or "school shuttle" to find companies that do this in your area.
Good luck - I hope you or your daughter find the best solution for the children as soon as possible.