How did this come in here?
As to the original topic, you should realize that most 7 year olds have the concept of Kosher and Traif deeply ingrained. Children relate very well to the untouchable concept.
When a child has frequent contact with close people who eat Traif, he will not be able to view non-Kosher as off the map. It will be more like we don’t eat it but they may. That is why the child is sneaking a piece.
Adding to this is the fact that most probably we are dealing with a BT, who may have the disadvantage in Chinuch of the children feeling that all this is a choice of their parents, rather than iron-clad.
When someone has such a situation it will take a lot more effort to give over the correct attitude to the child. It is hard to give specifics, but having more solid Frum aquaintances is one idea. More importantly, speak often and a lot of Hashem, the Torah, Olam Haba, S’char, Moshiach, Kedusha, Neshama, Matan Torah and Mitzvos.