I've seen similar behavior on my mother's box (Athlon XP 1600+, 768 MB of memory, Windows XP SP2).
The system was dog slow. Each click and every action took up to a minute to complete. No obvious resource hog could be observed under Task Manager.

Eventually, I've upgraded the IBM Proventia Desktop app (came with a VPN package) to a newer version, and the system literally recovered from a slow stutter to a normal (usable) pace.

But seriously, kudos for teaching your child to keep a healthy balance between intellectual and physical activities! I've recently became a parent, and this is also one of my main objectives.

Cheers & Best Luck,
XnPlater