Mature and Immature Faith

The word קטן can mean “small”, “young” or “immature”, and in this context מִקְטַנֵּי אֲמָנָה seems to mean “among those whose faith is immature”, since faith is an abstract concept that can’t be big or small, or old or young, but it can be mature or immature. Mature faith means that one takes his faith very seriously so that he doesn’t worry about the future because he trusts in Hashem, just as someone mature about decisions makes them seriously. Immature faith means that he doesn’t really take it seriously; he only believes superficially, but practically speaking he is worried because he doesn’t fully trust in Hashem, like someone who is immature and doesn’t take decision making so seriously.