The structure "unless" is used to mean "if not." In this case, the correct sentence is:
\[
\text{If children don't play any games, they will become dull and lazy.} \Rightarrow \text{Unless children play any games, they will become dull and lazy.}
\]
The verb form "will" should be used after "unless," and it needs to be in the present tense in the conditional clause. Therefore, option is correct.
Final Answer:
\[
\boxed{\text{Unless children play any games, they will become dull and lazy.}}
\]