My son learnt basic coding last yr when he was 10yrs old. He picked it up pretty fast as he was really keen in it and could also go online to learn further on his own. However, I worry about the impact of exposure to computer at such young age which has extending effects on attention issues. How do we curb that?

I think the problem with attention issues goes away when the child is trying to build something with code, rather than switching from one game to another looking for one that captures his attention. Coding is a deeply absorbing activity and I've seen our students lose track of time because they are so absorbed in coding their game/animation/website. Quite the opposite of short attention span, actually.