Puppy
noun
A child dog is a puppy!
こいぬ
Even though this is a jukugo word, it doesn't use the on'yomi readings. Both the kanji 子 and 犬 often favor kun'yomi readings, and this word is no exception. The reading for 犬 is the one you already know, and the reading for 子 as こ is a really common one (perhaps you've already learned that reading?). If not, just think about punching a puppy in the face, and giving it a KO (That's a knock out).
子犬は、かわいい。
The puppy is cute.
子犬はトレーニングがたいへんです。
Puppies are a lot of work to train.
子犬ごっこをしましょうよ。
Let’s pretend we’re puppies!