This article contains recommendations and you should take them as just that. Always use common sense and consult a physician for specific recommendations when it comes to anything related to yours or your child's health, fitness, and wellbeing.
Yes, But There Are Some Limitations
The occasional SUF session for a 10 to 12-year old riding in a fun environment with an adult riding along-side at a reduced FTP/target setting, without giving specific targets to the child, should be okay. Specific intensity sessions are not helpful or healthy for young people. No available research supports the pushing of specificity training until into the early teen years.
A SUF workout for fun every now and then is great!
Using The Sufferfest as a training tool for a pre-teen... NOPE!
What About An Older Child Then?
We do not recommend a 14-year old following a specific training plan, but to do various sports including cycling and most importantly to have fun! Learn how to ride a bike and spend time developing skills is more important than specific fitness at that age. Having them do one, at most two, 20-50 minute sessions each week at a maximum. More focus on neuromuscular work (like Half is Easy and Revolver) and maximal aerobic power (like just Do As You're Told and The Omnium) would be recommended rather than FTP focussed sessions.
But to reiterate - have fun, learn skills, and no need for a training plan yet!