Simulating 'Growth' Help

So basically I want to do something where say I have the players model as a kitten, but after playing for so many hours it will eventually grow into a full-sized cat. To do this I was essentially thinking to have the model set to scale up its size over time, then shut off after it reaches the decided amount of time so it doesn’t just keep growing forever. In animation its called a scale-tween, but I’m not sure how to do it for a game.

Ideally, but probably more complicatedly, I would have both the model of the kitten and the adult, and do more of a ‘shape-tween’ so that the model of the kitten slowly becomes the model of the adult smoothly and without any cut-scenes or breaks where you’re suddenly grown up. But I’d settle for merely having the same model the entire time simply grow in size as well.

I want to do this for the players character, not an npc. Hopefully there’s a way to do it that isn’t too complicated?
Thanks guys any help is really appreciated.

What I could imagine is too use Morph Targets.
With the Morph Targets you change the look from childish to muscular/ more defined.
At the same time you scale the model itself.

I haven’t tried this but theoretically it should work.

Morph Targets only work with the specific model though.