Most recommended solution:
replace OS with
A) Windows 8
B) Linux Mint or Similar
C) OSX as noted above
Windows 8 does have exactly 2 things going for it.
1) it does everything for you: it grabs email, news feeds, social network stuff
2) Windows 8(like the other OS's above) are far more secure. fewer viruses around, more locked down
I'd probably most strongly recommend win8, as its the most similar to what they are used to. win 8 can be used with the the other options suggested
Second most recommended solution install Firefox (and hide IE). EDIT BY MOD - Captain Ned - Forum Rule #12 violation
Third most recommended solution
Spybot S&D and Ad-Aware, I don't like these because they have a tendency to get ignored.
Fourth and least recommended option get them a physical firewall/router and literally write them a list of websites that they can visit, mommy style