How to stop toddler undoing Britax?

[User989546711]

Hope someone can help! My 2yo has learned to press the release button on the buckle or her Britax group 2 car seat and climb out while the car is in motion. We are trying to teach her not to but it's getting very annoying/dangerous as she won't take heed.

Anyone know of a product that can cover the closed buckle to prevent little Houdini scampering around in the back? So far a knotted muslin has been removed in seconds...