I've GMed for or played with a handful of players in the 10-13 yr range. Each one of them had difficulty staying focused for 4-5 hours, but their distractions to the table were minimal. Whenever they start to get disruptive, I use my Dad Voice to ask them to quiet down. That usually does the trick for a while. If needed, I will quickly explain a plot point or faction mission to them. If they want to wander around the store for a bit and miss some combat rounds, so be it.
We have to remember that these young kids are going to grow up one day. That 8 yr old disruptive kid might turn into a 5-star GM in ten years. It's up to us, the community as a whole, to teach and encourage them if we want our hobby/passion to thrive.
If it were me, I would focus on how to minimize the kid's disruption to the table, not how to remove him. Talk to Dad and try to work out a solution everyone is happy with.
Also, the suggestions for kids games and breaking up scenarios are great ideas.