Only during a baby's first month is its cry purely physiologically linked; from then on emotions are involved. Emotional contagion has been observed in children as early as two days after birth.

Milestones of Development:

1. At 1-3 months: infant gains the ability to raise his/or her chin from the ground and can turn its head from side to side and play with hands and fingers
2. At 4-6 months: baby rolls over
3. At 5 months: baby reaches and grasps while sitting on someone's lap
4. At 6 months: baby sits alone and may stand with support
5. At 5-9 months: first teeth appear
6. At 7-9 months: coordination improves
7. At 8-9 months: creeping and crawling usually begins
8. At 10-12 months: child pulls himself/or herself to standing position with furniture and walks with help
9. At 15 months: baby stands alone then gains ability to walk; he/or she throws things
10. At 18 months: toddler can walk sideways and backwards
11. At 2 years: child walks with a steady gait, jumps, runs in a controlled way, and can climb stairs with help
12. At 3 years: typically toilet trained, child dresses and undresses with simple clothing and can scribble
13. At 4 years: child prints first name and has stable preference for right or left hand
14. At 5 years: youngster coordinates movement to music
15. During middle childhood: gender differences appear

Girls:

1. More physically mature than boys of the same age
2. Superior in skills requiring flexibility, agility, and balance
3. Early maturation works against girls resulting in:
a. Lowered self-concept
b. Dissatisfaction with physical development
c. Sexual precociousness
d. Increased potential for drug and alcohol addiction
4. Late maturing girls are likely to be dissatisfied with their physical appearance and resent being treated as younger than they are

Boys:

1. Physically stronger than girls
2. Perform better in activities that require gross motor movement
3. Early maturation improves popularity and adjustment
4. Late maturing boys lack confidence, perform more attention-seeking behaviors, and are considered childish

Other factors related to good development are high socioeconomic status, a two-parent family, little visible disfiguration, and healthy parental adjustment.