When should I tell my 8 year old and 9 year old I’m pregnant?

My son is 8 and my step son is 9. They’re both very mature boys and have experience with this sort of thing. My sons father has a baby and my stepsons mom is currently pregnant with a baby.

3 years ago I had a miscarriage and I never told them I was pregnant until my son saw me sobbing and I explained to them “mommy had a baby in her belly but God decided it wasn’t time yet and the baby went back to heaven until the time is right”. They both reciprocated well and understood.

Now they are much older. I’ve been nauseas everyday and not feeling good. And I think my son is starting to worry why I’m always sick. He asks me if I’m okay and says he’s worried about me.

I am only 6 weeks pregnant but do you think I should tell them and also explain why it’s important not to tell others yet? Im running out of lies to tell my son why I’m always nauseas and exhausted.