Developmental milestones are important age-specific skills that most children can do at a certain age, and are used to help check how your child is developing in various developmental domains, or categories, the major ones being social/emotional, language, cognitive, physical/movement, and sensory. Things like rolling over, playing, scribbling, crawling, laughing, pointing, babbling, etc. are all important developmental milestones to keep track of.
Why Developmental Milestones Are Important
Developmental milestones offer important clues about your child's development. Achieving milestones at the typical age indicates that a child is growing and developing as they should. Reaching milestones earlier means a child is advanced compared to other children of the same age. Conversely, not reaching milestones or reaching them much later than peers of the same age can indicate that there could be a developmental delay.
The actual age when a normally developing child reaches a milestone really can vary. Each child develops in their own unique way, so there's no need to worry unnecessarily if your child isn't hitting a milestone right away, especially if they are hitting most milestones in other domains.
That being said, you are your child's best advocate. If you suspect an issue, it's always best to act early. So if you have concerns about your child's development, please contact your pediatrician.