Write a question about the following article: There were 458,057 households at the 2010 census, out of which 29.1% had children under the age of 18 living with them, 36.1% were headed by married couples living together, 16.0% had a female householder with no husband present, and 42.0% were classified as non-family households. 33.7% of all households had one or more people under 18 years of age, and 17.6% had one or more people who were 65 years of age or older. The average household size was 2.57 and the average family size was 3.42.

Question about the article:
Which groups in average were under 4 in size?