THC how are you? Was it as a result of your fall in London that lead you to hospital again? I hope you are all right. They are not going to be dismissive tomorrow at GOSH, I am sure. I agree the advice you are gievn about ds' wheelchair is bonkers. I apprecaite that they want him to keep moving as much as possible, as exercising the muscles should help, but really, there has to be a balance. He needs the wheelchair when you are out, he can move around home without it if he is able.....stupid people who do not think about what they are saying and the practicialities of it.
Oodles - Poor gait, poor proprioception, and poor gross and motor skills can very much be a part of this condition.,If you are really noticing instablity in his ankles I would steer away from a trampoline for now. I would get some boots and physio input and build some strength with physio exercises, then move on to controlled movement on a trampoline with an adult to support, otherwise he could dislocate or twist the ankles and cause more damage. Go to your gp, tell him/her what the OT said, bearing in mind they are not qualified to make a dx, and ask the gp for a referral to a rheumatologist, then you will get a dx and referral to phsyio if needed, or advice about what to do with things like building strength. It should not take more than a couple of months to see an rheumie if your gp will refer. Problems tend to arise if the hypermobility/symptoms are more compliacted, or if you have a gp from the dark ages! It is worth a try before you pay for a referral.
Misdee and lisa you seem to have been dealt the same strong genetic card as THC! Misdee does your dh believe it is not normal yet, or do we need to pop round to sort him out 
My ds is ok, but not brilliant. He woke up this morning and screamed in pain when he tried to get out of bed, his neck and middle of his back were extremely painful even to the lightest touch. I had to massage him gently, give him painkillers, carry him to the toilet, get him dressed, help him eat, lift him in and out of the car....but don't worry the dla say he doesn't need more care than an average 8 yr old!! [need humphing emoticon, but am too kanckered to humph] I did get him into school, as I think gentle movement is better than him just lying in bed, or sitting at home, but am leaping to the phone everytime it rings just in case. Although saga there, as BT currently burying phone lines to cottage, which invloved phone being cut off for a while, and trench they dug last week and have already filled in collasping, making a foot wide, metre deep hole which has filled with rainwater, and looks like a normal puddle, until you step in it!