My Little Boy 2ys 3mths , Was A Pre Term

my little boy 2ys 3mths , was a pre term baby 32vweeks . at that time only 1.30 kg now reached at 9. 10 kg. very much active. we are worried about his weight. no suuplimentary food provided yet. only home made. looking others of similier age we are worried. how we can improve his weight.