Hi, I have a baby boy 11 months and 10 days, who seems to be a little delayed on achieving gross motor skills. He never crawled, he hates tummy time, he just rolls over. He can walk if held by hands, but does not pull himself to things for standing. No equilibrium or balance. Cognitive abilities and fine motor skills seems good for his age. While I am sure his legs and back are strong enough for crawling and even walking, his arms and shoulders are not since he won`t use them at all for supporting the weight of his body. What kind of exercises should I do with him to strengthen his upper body and arms?