Depending on what your children normally downld (presumably music), you can add & remove keyword filters. Recommended would be .exe, .jpg, & .wmv Go to Tools>Options>Filters>Keyword & type in these words one by one & press Add each time. It would mean you may need to remove them each time you use it.

If LW is in your Admin account. Can't you make it so it's read only (ie: changes would need an admin password)? I'm not a windows user per se so I'm not sure about this. I should imagine you should be able to protect LW's option changes some way like this. If they have their own user account folder, then are you able to lock the LW preferences folder so no changes can be made?