"My mom bought a cute handkerchief."
I don't know how late this is but it's because かわいい is an い adjective, shown by the way the adjective ends. These adjectives don't need those extra particles. There are also の and な adjectives, like 大切(たいせつ)[な]もの or 一番(いちばん)[の]宝物(たからもの). い adj are easy to tell since they end with い but there's one adj (probably more) like 綺麗(きれい) which isn't one, because the い is part of the kanji(at least that's how i see it)