Does focalin (dexmethylphenidate) make your child stay up late at night?

Sometimes. Focalin (dexmethylphenidate) is in the the stimulant family, and insomnia is a common side effect of all stimulants. However, children with adhd, even unmedicated, have a fairly high rate of sleeping problems. Trying to take the medication as early in the day as feasible may help in minimizing this side effect.
Yes. Any of the stimulants can cause insomnia. In my experience, insomnia is less likely with Focalin (dexmethylphenidate) compared to the other stimulants. It is possible that the Focalin (dexmethylphenidate) is being taken too late in the day. Strattera, a non stimulant fda approved for add, could be an alternative. Insomnia is unlikely with strattera.