Final answer:
A child typically starts to smile in response to stimuli at around 1-2 months. This is a sign of early social interaction and emotional growth.
Step-by-step explanation:
A child typically begins to smile in response to stimuli at around 1-2 months of age. Infants at this stage develop the ability to hold their head up and start to show their first social smiles at their parents and familiar caregivers. It's a delightful milestone that signifies the beginning of social interaction and emotional development.