My 8-year-old-son is a mostly unwilling experiment with respect to this Computational Fluency site.
I set up his own ID, but I bring him to the computer and I log him in and we negotiate how many questions and/or how many minutes he will spend doing the work. I am a believer in regular short bursts but if the child in question decides to hang longer, so be it!
He enjoys taking a break and reading the awful jokes out loud. Sometimes the puns are not clear to him but he enjoys when I explain them.
In the end, parents will have to encourage and/or enforce the practice, but I’m frankly enjoying being able to trust that the system is showing him the right answers and I don’t have to mark the work sheet. It’s always better to immediately receive feedback to the right and the wrong answers.
I’ll keep you posted on how this goes.