Child support is typically terminated upon the minor child reaching the age of 18. Termination of support can also be brought about by the child marrying, joining the military or otherwise becoming emancipated.
Unfortunately, none of the facts that you have presented would lead to the termination of your child support obligation. So, to answer your question, the fact that they have had children of their own does not end your support. Having said that, if they become emancipated in anyway, your obligation would likely end at that time.
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