Your question somehow confuses me - growth/care requirements for which, specifically? Each version can have their own set of growth mechanics. Or are you just asking in general?
The only "growth/care requirements" you can influence is on the first generation in order to get the desired built-in character. For the Melody/Spacy Mix, check out this chart.
The future generation adults becomes a blend of the two parents, so that's how they will take on the appearance. You can still make the toddler and teen stage take on one of the built-in forms, but they would have something like the mother or father's headpiece, eyes, mouth, etc.
Otherwise just make sure its hunger and happy bar aren't empty!