Are questions about choosing specific martial arts disciplines for fitness purposes in scope?
E.g. choosing one for a young child to improve hand-eye coordination and cardio fitness, with minimal impact stresses or injury risk (Aikido >> Karate).
Depending on the specific tie-in to fitness it could be on-topic, but I would think that martialarts.stackexchange.com would be a much better resource.
Martial arts questions are on topic here, but something in the line of:
"Which martial art for a young child has the lowest injury risk?"
Would likely sprout a lot of different opinions. As an answer to this question heavily depends on the coach, the specific style and lastly the child. There is no clear cut – the one true – answer to this.
I think all the factors that make up a shopping recommendation request are applicable here and by that it should be off topic.