To sign all, take your open, non-dominant hand, palm facing you with fingers held all together, and just hold it steady. Then do the same hand form with your open, dominant hand, but make a sweeping, circular gesture with this dominant hand, first hovering above the non-dominant hand. As it makes the circular swoop in the air, make it rest on the non-dominant hand, palm facing you as well.
It is as if you are making a gathering gesture to include "all" in your discussion.
Teach your child the all sign in the context of family or friend gatherings, or simply when you are talking about groupings of food, toys, or other objects.
This is a useful flash card taught best in conjunction with group activities or games involving object groupings. Your toddler will learn that some persons and things can sometimes be given sole or exclusive attention, whereas people and things can be taken as a whole, in other contexts.