I don't think Symlin is indicated for use in children. I believe the medication is most helpful in folks who have developed some insulin resistance and are also looking to lower their TDD (at least that's what my endo told me when inquired about it; she said that my TDD was too low to consider using it).
Keep in mind that young children have BGs that fluctuate more widely. And while high BGs aren't wonderful, they are not nearly as harmful in small children as they are in adults. From what I understand and have been told, young children are able to better withstand high BGs (especially for short periods of time) and that it's really LOW BGs that you have to be careful of, as prolonged lows can interfere with brain development. This is one reason why youngsters have a larger acceptable range.
Have you experimented with square and dual-wave bolus features (assuming your son is using a pump)? For me, these have been lifesavers in avoiding those post-meal spikes.