"Los niños tienen que escribir mucho."
Translation:The children have to write a lot.
Not really. "Tener que" means "have to" in the sense of "must." What you wrote would be "Los niños tienen mucho de escribir."
Why is there a "que" in this sentence? Why not simply "tienen escribir?"
Tener que is a fixed expression, meaning have to.
Tienen by itself means they have.
Gamekkeut, I've noticed you go out of your way to answer sentence questions here. Thank you for this.
I'm not sure why someone downvoted you. Here one up and a lingot for making the forums better.