booster seat

So we finally put our daughter in a booster seat; but she put the seat belt under her arm and is able tp get out. She was getting her arms out of the car seat: this is worse because the belt under her arm doesnt lock. We tried telling her she has to stay io her seat....we showed how we wear our belts but she doesnt get it.
Any ideas on how to keep her in the booster seat. HELP!!!!

Re: booster seat

How old is she? Sounds like she isn't ready for a regular seat belt with the booster.