We have been using the Nalgeen Grip-N-Gulp water bottles for years for our son. We rarely experience any leaks at all, and when we do, it is only a little drip, not a major mess to be cleaned up like other sippy cups. We decided to go ahead and purchase the same cups for our 6 month old daughter when we started her on sippy cups. I wasn't sure if she would be able to figure them out, but it didn't take her long at all. I did remove the stopper at first and tipped the cup up to her mouth so she would realize that something was supposed to be coming out of it. I then replace the stopper and held it to her mouth again, and before long, she was happily drinking from it. These are the only sippy cups she uses (now 10 months old), and we haven't had any problems with them at all. Great cups!!