My DS (just 5) gained 1 lb last year, but they are okay with it at the ped. He is no longer extremely thin, though. (20%th?) He used to be "off the chart."

I recommend Ellyn Satter's work for feeding issues, though I should say that I have a thin child, but not one who refuses food.

The thing that concerns experts is that eating while distracted may seem good now, with a child who appears thin, but as a lifelong habit, it is risky.