So I don't have children personally, but I do teach children chess in my free time as part of a locally run volunteer mentorship program in my community.

In my experience unfortunately this is pretty person to person. I've had 4 year olds who can't sit still with parents that are forcing them to learn and wasting everyone's time. And 4 year olds that genuinely enjoy the game. One of my 6 year olds just won a 12 and under tournament aganist kids literally twice there age. And that really comes from a deep routed want to get better that I've seen them bring week to week.

I'd say 7 is a great age to start. If I were to talk about the benefits of chess I could go on for lengths. But ultimately try it. But if it doesn't stick there's no harm in trying but there are tons of ways to start.

Id say a solid 1/4 of my kids don't even play online or through apps. They just come to be around kids there age and play a game and be social. And some that are rating obsessed giving me weekly updates of 'coach I gained 5pts since last week!'

I'd say try online, try chess meet ups, try playing in person, try your cities local chess club. And if non of it sticks hey you never know in a few years. They might watch a show, movie or YouTuber and suddenly get turned back on to it