Gestation is the early development, from the time of fertilization to the moment of birth. The gestation period is different for most living creatures. In humans a woman's gestation period before her baby is born is 9 months. An for example an elephant usually takes 22 months. A mouse is only 18 days and a chicken hatches after 3 weeks.
This worksheet comes from the linked workbook and has this assignment and lots of other fun science worksheets related to the science names projects.