It's possible that your baby has begun to move around, they may have been crawling for some time and are quite possibly walking independently. They will have acquired the skills to be able to sit without support and furthermore, when your baby has been playing with toys you may have seen your child crouching or kneeling. When they play with floor toys, they sometimes sit on their legs to make it easier to reach the items.
All these skills have been helping your baby to strengthen the muscles in their legs and core, in addition the connections being made in their sensory and motor muscle systems are learning that their body can do more and more gross motor movements [1]
Your baby has been developing their locomotive skills whilst moving, however now they are starting to squat, their non-locomotor skills are being further developed. Non-locomotor skills are actions that take place when your baby is stable in one position i.e. sitting and standing. They use their arms and legs to bend and stretch into different positions without actually going anywhere.[1] At this stage your baby will use their arms to help them push back up, this will continue until your baby is more confident and has control of their motor movements.
Squatting is very functional, and it allows your baby to do all kinds of new things from picking objects up off the floor to being able to sit on a potty. The muscles in your baby’s legs stretch every time they squat and the more they squat, the further down they will be able to travel. Lots of muscles and movements are used to perform a squat: your baby will be working their core muscles to help keep them balanced, they will use their glutes to help travel down and extend back up again, plus they will need their hips, heels, knees and ankles to be able to track properly in order to carry the body in one movement. The strength that is being built in their hips, along with the ability to support their joint loads will help your baby to stand and walk.
Proprioception is the awareness of position and movement of the body. Your baby is now developing their sense of space, and their proprioceptive receptors are working hard to sense how far they need to stretch without falling forwards [2]. To create a successful squat, your baby requires balance and the ability to align their body. Their brain is receiving constant feedback which allows for more complexity in the movement whilst they practice [2].
The skills your baby is learning from squatting will lend themselves to many movements over the next few months. Their muscles will be further flexing and stretching whilst gaining strength. The flexibility that is created in their ankles and knees will support them as they gain the skills to ascend and descend stairs.
References:
[1] L. Woodfield (2004) Physical Development in the Early Years. Continuum International Publishing Group
[2] C. Hannaford (2005) Smart Moves, Why Learning is not all in your Head. Great River Books