My child is 1.5 years old, had maningitus when he was 3 months old.afterwards developed hydrocephylus..now he cant not sit independently.?

NEEDS CT/MRI OF BRAIN AND REQUIRE SURGERY - VP SHUNT. POST OPERATIVELY REHABILITATION IS REQUIRED

First Assess his neck holding if it is complete then work on muscles of lower back and lower limbs and also use upper limb activities these will help you in achieving future goals in a best way. 

VP shunt and perform passive-active daily exercises that strengthening the core muscle of the lower and upper extremities.

 that is  one of  late complecations  of meningitis its  hydrociphalus

need for  v-p shunt

Do some exersice for core muscles

Arrange for MRI brain   and if necessory arrange for VP shunting only if Post L/P   gait improves 

vp shunting! but must be evaluated first by a Neurosurgeon

to do brain MRI to roul out shunt malfuction

your child can not sit that caused by pressure which is made by high pressure csf to the brain and therefore i think the best approach should ventriculoperitoneal shunt operation.

does  it need a valve, i mean a ventriculoperitoneal shunt?