EB,
I just googled to see how difficult it was to get the info you require! Try this link
http://www.flightmapping.com/UK/Bristol/ It seems the nearest airport to you with Scheduled services to Norwich is Bristol! Rates look cheap enough if you book in advance, i think you said every 3 weeks, so that should get them in the £30-40 eachway bracket. Only one flight on a Friday though Landing at 12:20, are the kids old enough to travel alone? Failing that try
www.alanmann.co.uk/fairoaks/ for a charter service. Check your PM's for more info.