Are you concerned now because you would like to retaliate or the sudden in-wave of moral responsibility you feel?
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I'm not sure what your question actually is.
Are you concerned that your ex will lose her status due to not reporting that incident on her application and that if she loses her status she will take your children out of the country? Or, are you wanting to report your ex to USCIS.
If you have custody concerns you should probably talk to a family law attorney about that.