Asthma injection for a 3yr old

My nearly 3 yr old was seen today. He's on pred every 3-4 weeks plus a heap of other things. He's had extensive investigations and today they gently mentioned the possibility of a fortnightly injection. They were upfront explaining it's not licenced under 12yrs but they have some experience with 6yr olds, and its mega expensive etc etc....

I thought he said NDIGE (I am deaf!) but having done some reading I think the dr was referring to Xolair.

What experience to parents have with under 12s with this drug?? Should I be more worried its been suggested or more worried we've got to that point in under 3yrs???

Ruth