Try setting each user's LW to use a different port. If that's possible. If port forwarding is required for each account then so be it. If a program has been using a particular port, & then another program later or at same time tries to use the same port then it may cause issues. Depending on the setup of course.

Also consider this for your son's accounts: Tip: Purge the Downloads Queue!, as this will definitely freshen up LW & speed up startup times. Having too many incompletes & over 2,000 shares definitely takes its toll in OSX.