How to explain to a 3 year old that mom isnt coming back.

So, exwife became a heavy drug user, we split up, but not yet divorced.Against my better judgement I eventually started to let her see the kids again on the days I wasnt working and she was in town.One day, while high out of her mind on meth I told her that I wasnt letter her see the kids like that. In response she jumped in my car and took off with them. Drove them around for a couple of hours, then took them to the hospital and told the doctors I had tried to poison all of us with antifreeze. After dealing with DHR and them determining that her story was false and she was still high, I got them back.She's still doing drugs (shooting up ice, mostly) and I've got a DV case on monday from where she hit me in the face.I'm trying to have her rights stripped if possible. She's too dangerous on the stuff that she does.This all happened 6 months ago or so. My oldest (3) still asks where she is sometimes. I usually tell him that mommy is sick or I dodge the question.The kid has been through a lot. I dont want to crush him, but I dont know how to talk to him about it. What age do I need to be honest with him about what happened? via /r/Parenting https://ift.tt/2Quyxs7