think I can help you there. There is first of all the Worksop Juniors set up, they fish between 20 and 30 matches per year mainly geared up to the various junior nationals and regional competitions. This of course requires some dedication and parents willing to travel.
If you are not interested in that then there will be the Guardian newspaper readership interschools championships in July, being fished at Lakeside, the 3 match league usually run between June and August at Lakeside, Retford. The Gateford canal junior match held near the Lock Keeper at Worksop. You can find all the details about these from the fishing page in the Guardian. There is also the Schools national which will be fished at Hallcroft in July, this requires teams of 5 and details are on the Angling Trust website.
Aston Park fishery runs frequent junior matches, ring Alex the fishery owner for more details or better pop down, he is young and really helpful.
I will be running a junior winter league at Lodge farm - six matches between Oct and March.
There are a good number of lads and girls fishing and the matches are generally well attended
I'm a coach and my son fishes all of the above, if you need further details come back to me on these pages and I'll provide more info.