On the Tianxun (Skyscanner China) website, we use the common industry practice of separating the types of tickets as follows:
Adults: aged at or over 12 years old
Children: aged between 2 and 12 years old(not include 12 years old)
Infants: aged between 14 days and 2 years old (not include 2 years old)
Normally children have to be accompanied by at least one adult for boarding. For special cases of children travelling alone, it may be required to apply for Unaccompanied Minor Service. (Airlines will make arrangements to look after your children).
Airlines have different rules and prices for age classes and for children travelling alone, and ticket prices may vary as well, so please make sure you check your final passenger numbers and the rules for children travelling alone with the airline/travel agent you intend to book with.