Advice on telling my kids about the 5th

I have four boys ages 11, 8, 6, and 5.

This is my first time being pregnant with them being old enough to actually understand what that means, and I'm SO EXCITED for them! I'm kind of at a loss on how to tell them though!

Also would you advise to tell them after we tell our parents? I'm worried if we tell the boys before our parents the boys may slip up and spoil it, but I also hate the idea of them knowing last!