I'm worried about Collin.

Me

Yesterday we went to see my nieces aged 2 and 10 months, Collin wanted nothing to do with them and was very shy the whole time. At one point the younger one started crying and Collin panicked and cried also. He spent most of the time in my lap or coloring in the highchair. We have a playdate about once a week with my friends who have a 6-year-old and one who will be 2 at the end of the month. And it's always the same, every time on of the kids comes up to him, Collin will run to me and most of the time be upset. He dose great with most adults; He'll talk, interact and bring them toys or books! Am I just over thinking this? Can it be normal for them to be so shy at this age or should I start looking into intervention?