What Are The Exercises To Be Done For Physical Development Of A 5 Month Old Child ?

My daughter is 5 and a half month old (born Sep20/2010), she s is a perfectly healthy child with proper physical developments, At this age she is able to turn on her own, can turn and lift her head while lying on stomach, responds to sounds and actions, try holding objects on her hands, hold her feet while lying on her back, try sitting with assistance, raises her head when lifted. Only difficluty she faces is unable to hold her head completely when trying to make her sit or holding her in our hands, though she turns her head at ease at this stage and can hold her head partially(her head is also slightly large, 43cm dia & her weight is 6.5 Kg) . Her padeatrician is suggesting occupational therapy in order to assist her developing her neck muscles. Shall we give some more time to the child in developing her neck muscles or it is absolutely necessary at this stage to go for OT, Are there any other excercises that can help her in her development Would be grateful to hear your valuable suggestions