Or even just buying a few fun and dirt cheap physical toys - hula hoop, jump rope, etc. Staying in minimally decent physical shape is super easy and cheap - even more so for a child.
What are their parents, siblings, and/or friends doing in their spare time? Are they going out for walks or bike rides? Or are they glued to some media/social media device?
Sure, there are kids who will get physical activity regardless of nearby influences, but many will decide to emulate the behaviour of those around them.
The study was in Taiwan, not America. They have extremely good educational outcomes, the educational system is brutal, and the Chinese parent stereotype is also very much true. Screw off in Taiwanese schools and you don't even get go to high school, but end up in special vocational training schools - not that there's anything at all wrong with training for vocations, but I mention it due to the sharp contrast with the US, as well as the motivation it creates for kids to maintain more options in their future.
So if a student is out of shape it's because they're in school from 7 to 5, in cram school from 5:30 to 7, doing homework until 9 or 10, and then doing it all over again the next day. But they're also the type that would still be 100% willing and able to squeeze in more physical stuff if told to do so, especially when it's good for your overall performance - which it is.
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Beyond all this, I really don't understand the modern Western trend of rejecting personal (or in this case parental) responsibility for basically anything and everything. It's predictably leading to terrible outcomes in near to every facet of life. Literally any parent in any situation can make their kid go jump rope for 20 minutes a day. It's even fun. Even better, the parent or parents could even do it with their children.
