Personally, I'm careful about what I eat, I don't eat junk normally. I don't think anyone should; but I can go out to dinner or even a child's birthday party and know how to use an appropriate amount of insulin for a less healthy meal. I don't eat a low carb diet, nor a particularly high carb one, nor do I spend all day eating rye bread either. I have good control and am fit and active. Good glucose control does matter but there are specific considerations/targets for children and adolescents.
My best recommendations would be to have a look at this book. I found it useful even though I was an adult. I've read of lots of parents who find it great as a backup resource,
http://www.amazon.co.uk/Type-1-Diab...8&qid=1397076826&sr=1-1&keywords=ragnar+hanas
The second one would be to contact other parents of children with T1. There are some parents on here and hopefully they will reply but there is also a UK Children with diabetes list/forum/info site
http://www.childrenwithdiabetes.com/uk/
The UKPDS study mentioned above is a T2 study with average ages in the study in the mid 50s , they don't seem to have followed dietary advice in any case .http://www.ncbi.nlm.nih.gov/pubmed/
8840101) .