Hi Hayley, we have a horse and I've used the RDA myself so I might be able to help a bit. Apologies if you already know any of this.
Riding is a brilliant therapy/sport for children.
Worth looking in Yellow Pages for riding schools then seeing which ones are members of a reputable organisation that checks standards, such as the British Horse Society or the Association of British Riding Schools. Then check them out online with those professional groups to see they're not lying (some do!).
Ring to ask what age they take children from, and whether they have an RDA group that uses them (many do) that you could talk to or one they'd recommend. www.riding-for-disabled.org.uk/Locations.aspx?Area=En is a link to the RDA so you can check out possibilities.
Then visit. This investigation visit is vital - you're trusting your child's life to these people and there are a fair number of rogues or pretty nasty characters out there who'll take your money/charity's money and not much care what happens to your child. One RDA centre I went to had a head groom who would attack the horses if they so much as turned their head slightly, and would mock the disabled children mercilessly. Another yard used to whip the horses across the head if they misbehaved. Trust your instincts. Watch a few lessons. Is it smiles and sensible suggestions they use to encourage, or threats and whips? Walk away if you see angry violence being used on the horses rather than a more gentle tap with a whip to remind the horse to watch out for something.
Is the owner friendly, helpful, co-operative? The staff?
Is the riding yard fairly clean and tidy and safe?
Are the safety notices up?
They should insist on proper footwear and a really well fitting safety helmet which they'll know how to check for a good fit even if they can supply one rather than you buy one straight away. Even on a small pony it's a long way to the ground for a tiny child.
Are the horses relaxed, clean, well fed? Even an non-expert person can tell if a horse is all ribs or has untreated wounds on them (you'd be surprised what you'll find in some yards...). Are the stables clean and fresh-smelling or full of poo and wee (sorry, TMI!) Are any of the horses lame? You can tell this by watching them being ridden - they'll nod their head down when a sore foot hits the ground when it's trotting (listen - if the horse's feet are hitting the ground in pairs with a 'one-two-one-two-one-two' march, that's trotting, rather than walking or cantering/galloping).
Where would the child be riding? Big clean indoor arenas are best, out of the rain and wind, but a friendly yard with a safe outdoor school should be fine. Is the riding arena clean and well looked after? This is where safety and care really shows up. Broken fencing, big potholes in the sand, weeds round the edge, poo everywhere? Run while you still can!
Go away, think about it. If you feel uneasy, find another place, even if it's further away.
A good RDA yard should always have well trained and fully insured helpers to help balance your child, and a well qualified instructor to help teach them things that will help their particular disability. Don't be afraid to ask to see qualifications and talk about their level of experience, or ask if you can speak to other people who have been customers of theirs. A good person will be delighted you asked.
Hope that helps a bit .