I saw this in a brochure and don't know whether it would be any good, but thought I would mention it anyway:
Sunday 13 March, Reading Concert Hall - 12.30 and 2.30pm
Tickets £6 adults £4 children
One hour event "offers families with autistic children an opportunity to enjoy music in a relaxed and informal setting. Seating will be around tables supplied with pens and paper for drawing, at the front of the hall space for children to dance, ticket price includes refreshments"
Music provided by OSJ (www.osj.org.uk) Tel 020 7374 8485 for a booking form