Final answer:
The earliest time to introduce solid foods to a child is at six months of age, coinciding with developmental milestones like teething and improved motor skills.
Step-by-step explanation:
The earliest time a young couple can introduce solid foods to their child is around six months of age. At this stage, infants typically begin to develop the ability to pick up objects and transfer them from hand to hand, pull themselves into a sitting position, and display significant improvements in vision, almost matching that of an adult's. They also develop cognitively, starting to babble words like "mama" and "dada" and may show stranger anxiety. Importantly, at six months, babies often begin teething as deciduous teeth start to emerge, which coincides with the traditional timing for introducing solid foods.
Introducing solids earlier, such as at two months or four months, is usually not recommended due to the infants' developmental stage. At two months, infants are just beginning to hold their head erect and may only be starting to smile and coo. By four months, they can roll from front to side and sit up with support but do not typically have the necessary motor skills and digestive development to handle solid foods. Thus, six months is the key age when solid foods can safely be added to a baby's diet.