I would find an age appropriate response that is truthful with just enough information. The older they are, the more they will understand their situation and you’ll be able to answer more direct questions they may have.  For little kids, one of my go to’s has been “they are working to be able to keep you safe”. Above all, I recommend finding ways to support the love they have for their family by choosing not to say things that are disparaging about their family. You want to be a safe place for them and you no longer become that if  they feel like they have to choose sides.
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