Don’t try Graham unless you have an adequate range of plastic trim removal tools - should be available on EBay or Amazon.
Gently, gently would be my approach, ‘teasing’ the crease slowly.
If you have to push the trim tools down behind the panel ( as I think you will) strongly masking tape a length cord to the top to retrieve the tool in case of difficulties!
Good luck, and let us know how you get on, and stop feeding that son extra Weetabix! - otherwise you are going to end up with a ‘one careful owner - x careless children’ vehicle.
Kind regards,
Gareth.