Can anyone help. My son is seven months old and up until now he has been able to do things before he is supposed to. he could hold his head at a few weeks old. But the problem is now he is becoming "lazy". he cannot sit on his own and makes no attempt to. as soon as you let go he gets onto his front. same with crawling - he just pretends he is skydiving - have tried to get him to crawl by holding him and moving arms and legs - he would rathre roll to where he wants to be. Am i being worried over nothing? is there anything i can do to encourage him to sit on his own and crawl?