Crybaby
noun
You've seen that 泣く is to cry, so you can probably guess that 泣き is just "cry." You've also seen how 虫 is rarely a nice thing to call someone. So what's a mean thing you can call someone who cries? How about a crybaby?
なきむし
The readings come from 泣く and 虫. So long as you're okay with those two words you should be able to read this one too.
泣き虫コウちゃーん、ほら、コウちゃんの好きなトンネルだよーっ！
Hey, crybaby Ko-chan. Here comes a tunnel you like.
コウイチだけがビエトが泣き虫だということを知っている。
Only Koichi knows Viet is a crybaby.
ウチの子の高熱が中々下がりません。いつもは泣き虫なんですが、今は泣く元気も無いようで、心配です。
My kid's high fever doesn't seem to be coming down. She is usually a crybaby, but it seems like she doesn't even have energy to cry now and I'm worried.