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Asthma is the most common chronic childhood disease in the world. Most children who develop asthma have symptoms before they are 5 years old.
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
Hip fractures are the most serious consequences of osteoporosis. The incidence of hip fractures increases with each decade among patients in their 60s to patients in their 90s for both women and men of all populations. Men and women older than 80 years of age show the highest incidence of hip fractures.
Although puberty usually occurs in the early teenage years, the world's youngest parents were two Chinese children who had their first baby when they were 8 and 9 years of age.
There used to be a metric calendar, as well as metric clocks. The metric calendar, or "French Republican Calendar" divided the year into 12 months, but each month was divided into three 10-day weeks. Each day had 10 decimal hours. Each hour had 100 decimal minutes. Due to lack of popularity, the metric clocks and calendars were ended in 1795, three years after they had been first marketed.