My kids did sneak around and smoke, without my blessings, but they grew up to be honest, trustworthy adults. Now they are both in their late 20's and both have quit smoking -- and they are still honest, trustworthy adults. Kids can always quit smoking, and most do. Kids who are liars and cheats are usually lying, cheating grownups. Smoking is a behavior problem, cheating is a serious character problem.
I don't see much of difference. They lied to you when they snuck the smokes, right?
You can now only assume they weren't lying and or cheating about other things.