My grandson is 4 years old. He vomits up food, laughs vigorously shaking, will not answer when you call him, and shoves large amounts of food into his mouth His parents have to get his attention to respond to my questions and then he does not hold a conversation as fluidly as his twin sister. Are these signs of autism? His parents deny that anything is wrong. He constantly plays silently on his tablet and they say his is smart. When he was 2 years old, he would showed little emotion when the camera took his picture and his sister knew when to smile on cue.