For those interested in just the pets, if you have multiple characters, you can complete the quests and pick a different reward for each toon. Pets are account-wide, so unless you have a preference for collecting all of the Children's Week pets on a single character or wish to earn the achievement Veteran Nanny, you can collect all of them in the same week.
There's a total of ten Children's Week pets, spread out across three expansions (Vanilla, Burning Crusade, and Wrath of the Lich King). Unfortunately, Pandaria seems to be devoid of any orphans to help, at least for now. Maybe there will be new quests and pets in Pandaria and Draenor in the future.
Wowhead has a great guide that covers collecting the pets as well as the achievements.
Other helpful write-ups for Children's Week detail how to complete School of Hard Knocks. If you're like me and really find PVP unbearable, this achievement may seem daunting. Here are two guides that may help reduce any stress and anxiety, as well as tips on how to get it done - Wowhead's 'Children's Week Guide - School of Hard Knocks How-To' and Cynwise's 'The School of Hard Knocks'.
The achievements aren't necessary for collecting pets, but it's a good way to feel even more productive during this fun-filled week. Collect tons of pets and how about being one step closer to that Violet Proto-Drake? It couldn't hurt. Well, it might hurt your orphan a little. Battlegrounds aren't a friendly place for a little kid! ;P