When child support is calculated, it is based on net pay, minus payment for insurance, and for pension, but not for anything paid voluntarily like a loan or money put into an IRA or a 401(k). If you pay for health insurance for the kids, that money is not considered as part of the money for the child support calculation. If you have children with other partners, but don't receive child support for them, that will not be part of the calculation for this child. Child support is calculated based on the income of the non-custodial parent for his/her child(ren). Other children from other relationships are not part of the calculation, unless you are talking about the calculation of the income of the non-custodial parent. Children born first are first to calculate for child support. The other children's support are calculated after the monies taken out for the older children first.
If you are military, they will calculate it for you. You can always call Deparment of Healthcare and Family Services - child support to help you with this, free of charge.