Kids generally don't want to know about mom and dad's sex life. I wouldn't talk to them about it unless they asked. And then I'd do it matter of factly. Not make a big deal about it. If you don't do public displays of affection as a couple now, don't start with your other.
Me: 48 - Married, straight, male
Shiela: My wife.
Suzanne: My FWB
Adam: Shiela's LDR