I think you are asking how to tell someone to have fun.
"Ten divertido" is literally "you have fun." It is a command form.
A less imposing form would be, debes intentar a tener divertido, which is you should try to have fun.
Ven conmigo a mi casa y nos divertiremos.
It will be fun - será diversión
Te has disfrutado = Did you have fun
I have fun with you: Me divierto contigo.
"Join the fun, learn spanish" would be: ' Únete a la diversión, aprende español'
What fun! or How fun!
diversión
diversión
Divertirse
If Mexican is just Spanish then have fun! is : ¡diviértase!
Divertirse = to have fun. Me estoy divirtiendo = I'm having fun.
fun