Concept:Probability is the ratio of favourable outcomes to the total number of possible outcomes.Explanation:The ages are 2,3,3,3,4,4,5,5,5,6, so the total number of children is 10."Not less than 5 years old" means age 5 or older.The children with ages 5,5,5,6 satisfy this condition.So the number of favourable outcomes is 4.Thus, the probability is 104.Simplifying, 104=52.Answer:52 Option B.