Is the Lantus all at once? I would try splitting the dose. What rapid insulin is used?
11 years old for sure is a growing ever changing youngster, this causes havoc. Does his dinner have a lot of protein? I ask because this particular nutrient is the one thing I know will deliver a high bg for me in the morning.
To answer your title question - Dawn Phenomenon...How do you handle it? - My answer is to adjust my basal if/when it needs to be adjusted. But I'm a grown up, and basal testing is easier.