Though cultures around the world are different, children's growth and development are universally similar; all children progress through the stages of childhood in similar ways physically, emotionally, and socially.
Developmental milestones are the expected skills that a child acquires within a certain age range. However, these milestones can vary in the exact age at which a child will actually accomplish them. Your pediatrician checks your child's milestones at each scheduled developmental visit. If you have questions about your child's developmental progress, check with your pediatrician or a child psychologist.
Child Development Guide: Ages & Stages (Children's Hospital of California)
Ages & Stages of Child Development (Child Care Resource Center)
Ages & Stages: How to Monitor Child Development (Healthline)
Developmental Milestones Checklists Don't Always Agree (Boston Children's Hospital)
"Yardsticks" by Chip Wood: Excellent book for children's physical, social, emotional, and academic development for the ages 4-14 (Excerpt for 11 year olds) (Excerpt for 6 year olds)
Chores & Children (by Age) (American Academy of Child & Adolescent Psychiatry)