For most kids roleplay come naturally, but they ‘transform’ in high school age-range to adults, so its important to keep that flame lit!
They are in an age range where peer pressure is building and conformality increased in importance to ‘fit in’. This naturally causes a discrepancy for trying to roleplay.
I would say the age of 8 is ideal to start pen and paper roleplay, not puberty.

Still, if they are showing interest all is not lost! 😊
You, as the adult, will have to unshackle yourself and over dramatize the action and the monsters to show them its ok to play pretend and a lot of fun too. Before you know it they might have friends sitting at the table with you.
Attention span is definately a good point; don’t go for the classic three hr block, but start small.
A good way to play, I find, is to ask them what their character wants to do and how he or she would react and then tell them whats possible within the rules instead of making them worry about knowing the rules all the time. Be lenient.
You’ll find some great kids oriented adventures on DMS Guild if you take a minute to search.
Good luck! Happy to read more about your endeavor soon!