For as often as I drink from them I won't switch out my older nalgenes, but you might as well start out your kids BPA free. The Nalgene Outdoors website is a very cool place, more bottles and vials than you thought they made. Last month I was lucky to order a few flexible cantenes while they had a 50% off no shipping sale on (expired 31 August). I'm going to use one of these 32 oz flexible cantenes and see how durable they are, and I also snagged a 96 oz flexible cantene to filter water into around camp. Its replacing an MSR equivalent that looks pretty beat up after one season, which replaced a 30+ year old JanSport 1 gal flexible water container that probably cost me $1.98 for 30 years of use.

http://www.nalgene-outdoor.com/store/detail.aspx?ID=71
http://www.nalgene-outdoor.com/store/detail.aspx?ID=86

50% off made the buying easy, but even at the list price these seem like pretty good deals.