Sorry Neil, I have to disagree re claxons......
There is more than enough room for a couple of grandchildren to run riot as they should while on holiday to let off steam. There is a great park at Oulton Broad and another at Beccles as well as the pool, outdoor play area and nature reserve at WRC and loads of interesting, informative places to get them curious, such as the bird trail walk at Rockland Broad, the windmill, Hardley Mill, one of our favourites although pricey now to moor, just before Cantley, the ruins at Burgh Castle, etc, etc.... lots to get children interested in.... It has to teach them more about their country and heritage than sitting round a pool on one of the Costas???
And.... for me, there is nothing nicer than seeing claxons enjoying the Broads..... they are the future tourist industry after all!
As far as places to eat, I wouldn't disagree with any of the recommendations, Surlingham Ferry, Coldham Hall and Dukes Head, Somerleyton all excellent. Also consider Dilraj (can get takeaway) or White Horse, Loddon and Chedgrave, chinese takeaway at Beccles (the harbourmaster will give you the details) and the Wherry Carvery at Oulton Broad.