Motor – Gross
Moves both arms and both legs
Typical Timing & Development Window
Starts
1
wk avg
Median
8
wk
Std dev
±2
wk
Flag
12
wk
Visual Timeline & Milestone Benchmarks
Typical range (68% of babies)
Earliest typical start
Median milestone age
Pediatrician check-in flag
What these numbers mean
Starts
~wk 1
The average age babies first begin showing early signs of this skill. Before this, it's simply too early — there's nothing to worry about.
Median
wk 8
The midpoint age: half of babies have reached this milestone by here, half a little later. It's a typical target, not a deadline.
Std dev
±2 wk
How spread out the timing is. About two-thirds of babies achieve it within one standard deviation of the median (the shaded band, wk 6–10). Wide bands mean a normal range of variation.
Flag
wk 12
A gentle check-in point. If your baby hasn't shown this by around here, it can be worth mentioning to your pediatrician — most often it's still perfectly fine, just later.
About this milestone
Bilateral spontaneous movement of arms and legs indicating active motor tone and symmetric limb movement.
What to try & how to support
- 1. Provide safe tummy time and unobstructed floor play to encourage limb movement.
- 2. Gently move the infant's arms and legs in playful motions to increase awareness.
What to avoid & gentle reminders
- 1. Avoid prolonged confinement in containers that limit spontaneous movement.