What are they?
The term milestone was a name for early roadside stone markers. Travelers could see how far it was to the next town. Called mileposts or milestones, these stones displayed the distance in miles. The ideas of location and distance can apply both to roads and to development. For development, the location is not a town but the event of birth, and distance is not measured in miles, but in time — weeks, months, or years of age. An infant milestone marks the distance is the time between birth and some other event.
Firsts are important
Developmentally, milestone implies travel is in one direction and away from birth. This is how chronological age is understood. There is no going back — except in time-travel movies and books. Milestone has a narrower meaning than chronological age. A milestone generally refers to the first time that a new developmental feature appears. For example, taking one’s first steps is reached the walking milestone. You may walk unassisted many times thereafter. The milestone is that first occurrence.
Milestones can be easily missed
There are many firsts for a child, but only some get referred to as milestones. Why? Partly it is a matter of how noticeable an achievement is. Rolling over is hard to miss, so it appears on nearly every list of milestones. On the other hand, rocking back and forth on hands and knees is rarely noted because it is more subtle. A knowledgeable observer will notice more milestones than an untrained observer will. The more you know about infant milestones, the more you’ll notice about your baby’s development.
Very common, but not universal
The term milestones used to be reserved for events that were deemed ‘universal’ and experienced by everyone. In truth, most developmental events are not experienced by absolutely everyone. For example, the most babies use hands-and-knees crawling, but not all do. Milestones are better considered as those developmental events that are very common, not necessarily universal. Crawling certainly counts as a milestone if we use this less rigid criterion.
The bigger story
Lastly, many milestones are developmentally important. Walking, for example, dramatically increases one’s mobility. Other milestones don’t have such obvious importance. Even so, they matter. Rocking back and forth on hands and knees is subtle. Reaching such a milestone is a building block for a later achievement, learning to crawl. Learning to crawl, in turn, helps develop balance. Balance enables walking.
Infant milestones are near-universal age-related events. They signal important change and growth in a baby’s life.