Ds is 19 months, he's got a few words he can put together and generally is on track with milestones as far as I'm aware. I have noticed recently that if i ask him a question where he needs to talk a bit to answer he's started rolling his eyes back in his head while he's talking. Is this normal? I'm assuming it's because he's really thinking of what he wants to say even though it's coming out as babbles still. Should I be worried?