Using one hand to hold a cup is so fantastic! It is the start of your toddler being able to use both hands to do different tasks.
It will take a while to master holding a cup with one hand, but while this is happening, your toddler will realise they can use their other hand for something else.
This will support them in other feeding tasks, such as holding a plate still while they scoop food, and cutting with a knife and fork.
For now, your toddler is concentrating on how to hold a cup steadily and drink without dropping it.
Your toddler will need a lot of practice holding a cup. You might need more cleaning equipment than ever before, but it is well worth the patience and time you find to support your toddler through this stage of development.
They are now relying on using one hand to lift the weight of an object that they used to lift with two hands. This will demand a higher level of strength in your toddler’s fingers, hands, wrists and elbows.
The palm of their hand will wrap around their cup while their thumb and fingers clasp the cup in place – this is known as a cylindrical grasp, or power grip.
Cups come in an assortment of shapes and sizes, and your toddler will adjust their grasp to match their hand size and the size of the cup they wish to pick up. This means your toddler needs to think and plan their movements to achieve a secure grip.[1]
Once the cup is in place, their wrist and elbow joints will work together to help lift the weight of the cup and coordinate the movement of bringing the cup to their mouth.
Vision and movement must be coordinated to be able to hold and use a cup with one hand.
Being able to pick up a cup with one hand requires good vision. To properly grab their cup, your toddler must control their reach and grasp while keeping their eyes on the cup and its position.
Reference:
[1] Edwards, S.J., Gallen, D.B., McCoy-Powlen, J.D., Suarez, M.A. (2018) Hand Grasps and Manipulation Skills. Second edition. Slack Incorporated.