@boomerang,
I'm a nurse in a children's hospital. I don't see a lot of Singulair. It may just be the pediatricians in my area. I see a lot of Flovent, though, which is the same thing as Flonase. I'm not familiar with behavior side-effects with it.
As was mentioned, though, people vary widely in how they react to meds.
There's nothing like a really good pediatric pulmonologist.
And as I'm sure you know... when in doubt about an asthma attack... don't wait around.. go on to the hospital.