Practice is signed exactly like drill: form your non-dominant hand into a fist, with only its index finger sticking out laterally, pointing to the other side of your body. Then take your dominant hand, form it into the letter A sign, and run it left-to-right and vice-versa, right behind your other hand's index finger.
It is like you are sharpening a tool.
Teach your toddler the practice sign when they are going through music school or they need some practice with their math, sports, or other skill-building activity.
Teach your child this sign to emphasize the importance of practicing any skill, whether it is physical, verbal, artistic, and so forth.