As you watch your toddler or preschooler play with his toys or test the limits you have set, you might not realize it, but your child is developing along principles set by Dr. Abraham Maslow. Back in 1943, the Brooklyn-born psychologist described children's development as a journey toward their full potential, or "self-actualization." He pictured this progress as a pyramid with five levels. A child's most basic needs are at the bottom and most advanced ones at the top.