Ughhhh... so hard to let go of some of those sweet times, isn't it? I remember feeling really sad, oddly enough, when I bought a potty chair for my daughter. How dumb is that??
I've always been super aware of my kids growing quickly. I had older siblings and friends with children that always said, "You'll blink and the time will be gone. Cherish every moment." So I tried to, and even so, I look at my kids now and it feel like a flash in time.
I slow down as much as I can and enjoy the time I have with them and the stages of development that they are in. You just have to realize that after one wonderful age and milestone there's another with new experiences and things to appreciate. And you have to realize the part you play in letting them become who they are by allowing those experiences to happen and guiding them through.
Take your time to grieve the stuff you will miss and what you feel sad about, and then embrace the next step and all the fun things age 1-2 will bring!
Hugs, mama!