i-adjective
Colloquial, often affectionate or childlike way to describe something as small or tiny. Derived from ちび (small person/thing) with the adjectival ending っこい.
この犬、ちびっこくてかわいいね。
This dog is so tiny and cute, isn't it?
ちびっこい頃はよくここで遊んだ。
When I was little, I used to play here a lot.