、。
Don't go too close to the pond — you might fall in.
Literal
Fall-[if-と] it-won't-do [because-から], too-much pond [to-に] approach-don't.
~といけない ('if X happens it would be bad / you shouldn't let X happen') is a fixed expression warning against a bad outcome. から here is causal ('because'). The final 近づくな is the plain negative imperative. Classic warning-to-a-child construction with stacked causality.