Sorting is an easy concept to model for infants and toddlers.

Place five green grapes and four red grades mixed in front of your baby.  Then say, "I will get the green grapes and place it on this side."  Get the green grapes and place all of them on the right side.  Then say, "Now the red grapes are on the left."  Then say, "The green grapes are now all in one group."  Point to it.  And follow it with, "This is the group of red grapes."  You can use this as an opportunity to model the concept of more and less by saying, "The green grapes are more than the red grapes."

You can use red and green apples to illustrate sorting concept.  Or you can mix fruits and vegetables also or a mix of toys.  Lego or Mega blocks or wooden cubes are good models to use to illustrate math concepts.