I've told a terrible lie 😔

Marie
Have any of you second time momma's had to explain to an older sibling "Where the baby comes from?" My daughter will be 8 a month after my son is born and instead of telling her the truth I told her they come out of the belly button because she's still so sweet an innocent and I know she'd have a little freak out followed by a thousand bizarre questions. I plan on telling her closer to time for delivery I just need to come up with an elementary explanation.. The rest I plan to write off with the "You'll understand more when you're older" line. 
EDIT: Some of you perfect women seem to have misunderstood the post.. I clearly stated that I plan to tell her HOW.. The purpose of my question was to determine the best way for ME to go about telling MY daughter in a way specific to MY parenting/HER understanding and I simply wanted ideas from other mothers who have experienced the same. It wasn't something that I wanted to discuss at the time while I was reading the sugar contents on a box of cereal down aisle 9 in the grocery store so I settled it with a bogus answer that worked for me when I was a kid.Â