It refers to the number of birth event(s)1 (regardless of child's nationality) by the mother and adopted-in children2. It excludes stepchildren, stillbirths and children who have passed away or are adopted-out before the birth or FIA3 of the child whom you are seeking reimbursement for.
1 Twins are considered as one child order
2 Adopted child must be below 1-year old at point of formal intent to adopt
3 Formal intent to adopt
*If the child you are seeking reimbursement for is born and with estimated delivery date and formal intent to adopt before 1 Jul 2017, please refer to here for definition of child order.