in order to answer your question few things needed first was your child able to hold his head at the age of 3 months ? does your child choke a lot? does he have a recurrent respiratory infections ? does he talk , smile , laugh , able to play ? did he was able to sit and walk and lose these abilities? if the problem is only motor ; he can t sit or move properly, then maybe the physical exam shows hypotonia ( no tone or decreased tone ) which some times come as an islated disorder , or maybe accompanied by other findings which need to be investigated thoroughly, because many disorders can cause that . but physiotherapy can be helpful , schedule with an expert physiotherapist and learn how to do it and do it on regular basis 3-6 times a day. start with the back muscles , because if your child couldn t sit , he will not walk , he needs a good back muscles .