To understand how kids grow and think, we can look at the stages created by a smart guy named Piaget. He showed us different steps in how children develop their thinking skills. Here are the main stages and some fun ways to check how kids are doing at each stage:

1. Sensorimotor Stage (0-2 years):

   • Object Permanence Tasks: One way to check if a baby understands that things still exist even when they can't see them is to hide a toy under a cloth. If the baby looks for it, that's a good sign! This usually happens around 8-12 months.
   • Morris Water Maze: This is a test that helps to see how well a young child understands where things are in space.

2. Preoperational Stage (2-7 years):

   • Conservation Tasks: These tests help us see if kids understand that changing the shape of something doesn’t change how much there is. Kids usually start to get this around age 7.
   • Egocentrism Tasks: The Three Mountains Task is a fun way to see if kids can understand things from other people's viewpoints.

3. Concrete Operational Stage (7-11 years):

   • Class Inclusion Tasks: This check looks at whether kids can sort things into categories, like understanding that a dog is also an animal. Kids usually get this by age 8.
   • Seriation Tasks: Here, we see if kids can put things in order, like sizing objects from smallest to biggest.

4. Formal Operational Stage (12 years and up):

   • Hypothetical-Deductive Reasoning Tests: These tests are for checking logical thinking by asking kids to solve science problems.
   • Pendulum Problem: This task looks at how well kids can ask questions, make guesses, and test their ideas to find answers.

Piaget noticed that about half of kids start to think in these advanced ways by age 15. This shows us that every child grows and learns at their own pace!