You can insure a child alone without an adult being covered also.
For quotes, enter the child as the applicant. For multiple children, enter the youngest as the applicant and enter the others as additional children. Do not use the spouse field.
Some companies allow all the children to be on the same policy, but others will require one application and policy/certificate per child.
If you have more than one child to be covered without any adult on the policy, try entering one child at a time. Extra quotes may appear becuase of the one child per policy rule of some insurance companies.