belt up
To anchor or fasten someone in place, as with a seatbelt in a vehicle. A noun or pronoun can be used between "belt" and "up." OK, the kids are belted up—let's hit the road! Can you please belt the baby up in her highchair?
belt someone up
to secure someone with a belt, such as a seat belt in a car. I had to belt her up because the seat belt was so complicated. We belted up the kids securely.