What sort of level is he at pre-meal?
Have you tried pre-bolusing to give the insulin time to get to work before the food gets in stream? Many adults do this to avoid spikes, but obviously discuss with dsn to make sure it's appropriate for a wee one.
Less than 8g carbs seems very small. Is there a chance the lack of carbs is forcing him into ketosis, turning the protein through gluconeogenisis into glucose leading to highs at unexpected times after the bolus has worn out?