What is your relationship to the parents? Are you a grandparent? Have you spoken to the parents? There is not really much you can do except teach by example. If you think it is appropriate and you are willing, file for guardianship or custody. For that you would need an attorney. No lawyer here would be able to tell you how to make the parents be better parents.
A lot more detail would be needed to advise you. You should probably talk to an attorney if you are asking a legal question, i.e. should I/can I seek an adoption or guardianship of this child. If you just want the parents to be more involved and are seeking advice on how to do so, you'd probably do better asking a therapist or counselor. The court's can do little to force a parent to actually provide care for a child if the parent does not want to. The ultimate remedy for a parent who cannot/will not take care of his or her child is to terminate parental rights -- this remedy is not a very effective tool if the parent does not care.
I hope you are the grandparents. If you are not then you better go to a lawyer and discuss theses facts. You need to perhaps take some legal action here. You have not said how old the child is.
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