"I had a size small Zipadee-Zip at the ready for when we needed to stop swaddling - which we did, when Jeriah was around 6 months old. The transition to his Zip was seamless! It only took a night or two to adjust. He then graduated to a size medium (pic included - from when he was 9 months old), then to size large. Now he is 21 months old, and I just got him a Flying Squirrel. I thought it would be too big at first, but he loved it and it fits just fine! It helped that it has ducks on it - his favorite thing in the world is Howard, his duck wubanub (you can see him in the younger pic!). He now wants to wear his Flying Squirrel everywhere, he sleeps in it, plays in it, he even wore it to the store today. I love the optional hand/foot coverings of the Flying Squirrel. Thanks for making such cute, cozy products! My kiddo and I are crazy about them! "