Hoping others have some tips to share!
My DD has had trouble learning to walk, partly due to her being hyperflexible and partly because of weak core muscles. Shoes have helped the hyperflexibility and lots of reaching/stretching got her walking in the end (we saw a paediatric physio when she was younger who recommended this).
She's now just turned 2 and still struggling a bit. We're waiting for physio but in the meantime I'm trying to think of things I can do that will help her, the stretching and reaching for things seems a little young for her, but doing sit ups seems far too old! If anyone has any experiences to share I'd be really grateful.