Is it fine if one introduces 5 year old to adventure sports. I am planning to go paragliding, do you think it is advisable to have my kid along under professional's guidance?

Well, if the company that organizes the activity allows for your kid to go along and they are a legitimate company, you can consider. But from what I know, most adventure companies especially if it's kindda high risk like paragliding, 5 is too young and the liability is too high. Maybe you can start small, like going on a flying fox or one of those guided trapeze activities.