My kittens have little hangy tummies?

they are 7 months old, eat 55 grams of kibble each a day (the amount for a 3kg adult cat) they never have treats or anything like that, since they were neutered we got advised to swtich them onto adult cat food rather than kitten as kitten has more fat in it but they have little hangy tummies ?(not huge!) they are tiny everywhere else do you think they need more exercise? i have aalready reduced thier food intake since they were neutered, i'm thinking that cos they're so small everywhere else it makes thier tummies look bigger?