My Baby Is 6 Months Old And She Is Premature,

My baby is 6 months old and she is premature, since birth she did not take mother milk instead she is taking Pre-Nan Nestle milk. At the time of birth her weight was approximately 01 KG, now her weight is 5.25 KG. We also giving her wheat cerelac with Pre Nan milk (Mix of milk and cerelac) since 1 week and she is digesting. Now after 6 months which formula milk can be given to her and any other supplement? Either continues to Pre Nan?