stealing 3 year old

my son is nearly 4 years old and over the last 4 weeks he has startded stealing can anyone help me stop this

[mylittlelammy]

What is he stealing? I tried early on whenever I brought my son out to the gas stations or grocery store that he may get a lollipop, and I give him the money and explained that he had to give the lollipop to the cashier so she can ring it up and then I would give him the money to pay for it. Worked like a charm, now he loves going out and knows exactly what to do and he never tries to walk out of the store with out paying.
If your child knows what he is doing is wrong, maybe he is just trying to get a reaction from you.