"Don't let the forest in It'll take you, and you'll give in The trees will whisper low And you'll never want to go"

Here are a few options:

"Don't let the forest in, with its wild and savage heart Lest you lose yourself, and play a brand new part The forest represents, the unknown and the free But beware, for once you enter, you'll never be the same, you'll see"

"Don't let the forest in, with its whispers and its shade Lest you get lost in the secrets it conveys The trees lean in, their branches like skeletal hands Reach out and claim you, with a forest's silent commands"