I've tried but they keep saying I cant

First who are "they"

But several things,
1. have you filed for dependent SSI payments, they should receive money if their father is receiving SSI

2. you get a child support order from the court, it will be set at a amount according to his current income. ( so it will not be alot) the issue is collection

If SSI is the only income he has then "they" are right. SSI is the only thing that is not able to be counted as income for child support so an order can not be made. If there is already an order and he went to court showing that he is on SSI then the order would have been stopped and any arrears are not collectible either. What you can do is contact the social security office on Monday and ask if your child can also receive payments because the father is on SSI. Sometimes they can and sometimes they can't but you have to ask the office to find out where your child falls.

There are two types of social security disability. One is SSDI/Social Security Disability Insurance / and this is restricted to individuals who have worked and now find themselves disabled. The other is SSI/Supplemental Security Income/ which is a form of benefit for individuals who have never worked. The latter is often viewed as a form of social assistance.

If a parent is on SSDI and is responsible for paying monthly child support payments, there is a chance that the payment can be taken from their SSDI proceeds.

In the case of SSI, the custodial parent has no right to any of the proceeds from the disability benefits. They can also not have any back payments they may be entitled to, taken for this reason.