Final answer:
The best response to address a mother's concern about her 3-year-old's slowed growth is to explain that children's growth is hereditary and size can be influenced by parents' stature, though growth monitoring is still important (b).
Step-by-step explanation:
When the mother of a 3-year-old expresses concern about her daughter's slowed growth rate, the most informative response based on the information provided would be: "Children's growth is hereditary. She may be of small stature like you." It is noted that children who are smaller than typical values for well-nourished, healthy children may not indicate any health issues, as stature is determined by genetics, as well as the environment.
Children of small parents often tend to be smaller. However, as toddlers experience decelerated growth in weight and height compared to their first year, any substantial deviation from expected growth patterns still warrants a discussion regarding nutrition and overall health, considering that 3-year-olds are still growing, albeit at a slower pace than during infancy.