Erhh... yes.
Not habitually, only if for example (and this has happened to us at least twice) we're on one of our ridiculously long bus journeys, I've got diet coke and J has left his water bottle somewhere/run out before we get to our stop. We bus everywhere, we try to get to Orrell a few times a week to see friends which takes around an hour and a half in okay traffic, if we go to Skem to see my Dad it takes another 20 minutes, if we go to St Helens it's at least an hour, you get the idea. So yeah, if we're stuck on a bus and either of them are thirsty and I've buggered up drinkwise, they have sips of coke. I can't say I'd give either of them their own fizzy pop, not for a looong time. Both prefer water, my oldest really hates fizzy stuff. It's only been the past year I've drank diet coke, I've always preferred water to anything else.