Donnamum,
The HbA1C is an indication of how good/bad blood glucose levels have been over the past 90-120 days, so the way to get it down is to improve blood glucose levels on a daily basis. The more highs, the higher the HbA1C will be. Your child's diabetes team are the people to ask about insulin levels etc. From personal experience I can say that 8% is not so bad for a child, I think they usually like to see 7's, but not usually lower (ie 6's) because of the risks of hypo's, which can affect children more badly than adults because their brains are still developing.
Anyway, if you are worries have a chat to your hospital team, I'm sure they will be happy re reassure and advise you.
Sue