Valve is letting Steam users sign up for their Family Sharing Beta where families can share games across user accounts and PCs. I don't have a ton of games I would recommend for kid play but I have a few like Plants vs. Zombies and Portal 2 that are not too graphic so I decided to check it out. You can sig up and get information about Family Sharing on the SteamPowered.com support site. Once you have you beta access, open Settings in your Steam client. Not the website but the actual client. On the Account tab click 'MANAGE FAMILY SHARING & DEVICES' then 'AUTHORIZE DEVICE' in the 'Authorized Devices' popup. To enable other devices, repeat the 'AUTHORIZE DEVICE' setup for each other device. Friends and family don't need to be part of the beta to be authorized. If you get a 'No authorized devices found.' you haven't authorized any computers in the Steam client.
Sweet! It's an XCOM: Enemy Unknown free weekend. Check out the game that has been consuming all of my gaming time as of late. Here's a little tip I noticed a couple of days ago to help you against the heavies. If you can get on top of a building and then position characters at the top of all of the ladders the heavies can't get up. This is especially good against berserkers. If they are standing against the wall they can't see you to shoot you when you are on the edge of the roof so move your characters around until they can spot them to shoot or lob some grenades over the side. This doesn't work against robot enemies or thin men as they can jump up to higher levels. Other tips... build up your Interceptor weapons and features so they can shoot down alien crafts and don't spend a bunch of money on laser weapons except maybe the sniper rifle.