Microsoft is discontinuing updates and support for XP next April 2014. So without security updates that will mean XP users will have to be very vigilant for vunerabilites.
It's probably better if they learn to use W7 which will see them through to 2020. A new pc with W7 can cost less than £300, Depends really on what they want to learn and do with computer.
(Will certainly save you any embarrassment and worry - they'd be bound to start asking you to help them with the old xp laptops).
You could put your xp laptops back to factory settings and sell them (even non booting laptops sell for the spare parts). Get an idea of how much by looking on ebay to see what they are selling for.