First words, first steps, smiling, sleeping through the night, solid foods, and potty training are all huge milestones to celebrate! Each one represents a major developmental stage, and recognizing them is such a wonderful way to appreciate the progress.
I also like to celebrate the ' invisible' milestones, which are often no less significant: that first time they show empathy or understanding, an interest in a new activity, or a new found skill like pouring their own milk! These little achievements are so rewarding and deserve some acknowledgment too.
It's such a nice idea to truly savor these moments and appreciate the unique phase before rushing onto the next one. After all, they grow up way too quickly!