There are multiple methods available for grandparents to provide care for their grandchildren. One is kinship adoption, which is permanent and irreversible. In an adoption your child's parental rights are terminated as well as their legal responsibility to support their child. So, in an adoption, your children would not pay support payments to you.
Other than adoption, the two primary options are legal guardianship and allocation of parental responsibilities (custody). In Colorado, guardianship is handled by the probate courts and and allocation of parental responsibility (APR) is handled by the family law courts. If this is a dependency an neglect action, the court would have power to enter orders for guardianship or allocation of parental responsibility.
The main difference between an APR case and a guardianship beside the court that issues the orders is that in an APR case the judge likely may allow the parents to have parenting time and will determine who can make what decisions, such as where will the children go to school and who can medical decisions to name a few. Joint decision making is also possible. Guardianships on the other hand are subject to a guardianship order, and except as limited by the guardianship order, give all the powers to the guardian.
Finally, to answer your question, it is impossible to know exactly how much you will be reimbursed based on the facts provided. In an APR case, the parents will pay child support. You can review Colorado's child support guidelines based on the number of overnights, income of the parents, and other factors. Colorado also has a calculator that you can use to calculate child support payments.
As for a guardianship, the issue of payments are not normally addressed by court. (The court has a lot of leeway, so they can be.) So, it is hard for me to give you guidance on expected payments in a guardianship case. Generally our attorneys recommend pursuing an APR case for this reason.