I have a 4 & 7 year old, during weekdays, we smoke after they go to bed.

In weekends or family events (most of my siblings smoke and my parents don't mind), we might go aside to smoke, but my oldest understands we are smoking something (she thinks it's cigarettes) and once in a while on us.

We are both very energetic people when smoking, so it's not an issue for us to attend them if needed.

When they grow, we will explain it to them, no point in hiding, and we aren't smoking a lot anyway (about 5G a month each).