Were relatives watching the children?
What age ranges were covered?
Without more information, the graphs are meaningless.
Maybe it's due to children having more unsupervised, outdoor play. Maybe it's due to relatives watching children more. If the age range is 0-5 years, the results are astonishing. If the age range is 0-18 years, then perhaps it's just a remnant of the shift from rural to urban populations, and the decrease of outside-the-home time by teenagers.