De is mandatory between permettre and an infinitive. The right form is ne vous permettent pas de le faire.

A few comments:

• Despite its final S, the word tennis is singular here so that must be written au tennis, not aux tennis (you don’t play "tennisses").

• This is addressed to a kid so the vouvoiement is unlikely.

• Permettre de le faire can be simplified to le permettre, l’autoriser, être d’accord or simply vouloir.

That leads to:

Si tu veux jouer au tennis mais que tes parents veulent pas, je peux t’aider.