Emotion and behavior are based on the child's developmental stage and temperament. Every child has an individual temperament, or mood. Some children may be cheerful and adaptable and easily develop regular routines of sleeping, waking, eating, and other daily activities; these children tend to respond positively to new situations. Other children are not very adaptable and may have great irregularities in their routine; these children tend to respond negatively to new situations. Still other children are in between.

At about 9 months of age, infants normally become more anxious about being separated from their parents. Separations at bedtime and at places like child care centers may be difficult and can be marked by temper tantrums. This behavior can last for many months. For many older children, a special blanket or stuffed animal serves at this time as a "transitional object" that acts as a symbol for the absent parent.