다(가) 보면

Used to make a threat or a promise (depending on context) that if an action occurs for some time something will happen.

The subjects of both clauses must be the same.

It's only used in the future tense, and the second clause usually ends in (으)ㄹ 것이다, 겠다 or (으)ㄹ 수 있다.

You can think of it as saying something like "If you don't eat your vegetables you won't grow big."