I have double hung windows with 2x6 construction which leaves a pretty deep window sill. The unusual situation is that I have a child with autism who likes to climb the windows at night - the sill, then up onto the middle sash, and hand from the curtain rod (I have actually installed pull up bars as curtain rods now as they don’t get destroyed).

I am wondering if there is a type of window insert perhaps with integrated blinds that could be installed inside the existing trim, which could be more flush with the inside wall so there would be no sill to climb on? I imagine it wouldn’t be able to open properly so this could not be done to code?