My son will be 14 months in next week. His weight is 9.6 kg. is he underweight?also he is very slow in development. till now he is not able to stand on his own. he walks only whne holding both hands. he is not interested to pull the things and stand also. hw was born in 35 weeks 7 days. he started sittimg on his own from lying position after 10 months. he doesnt do conventional crawling. he moves with pulling both legs and bottom on the floor.otherwise he is a very happy and active baby. is the delay in standing and walking normal? when will he be able to stand and walk on his own? please advice what to do.