That's interesting, NLWY, I am sorry for making incorrect assumptions about your faith. From a purely anecdotal basis it does seem to me that a lot of people who object to this sort of thing are doing it for nostalgic reasons, rather than religious ones, iyswim?
I can understand your annoyance at your nephews not knowing what Lent is much better than I can understand your annoyance at Cadbury's egg hunt.
I remember when I was at school, my mum (who is not religious) got very annoyed because I wasn't learning "proper" hymns. I was, they were just different from the hymns she sang at primary school, which in turn may have been different to the ones my grandmother sang.
My oldest relatives who would be much more likely to have dyed/painted chicken eggs as children, than exchanged chocolate eggs at Easter. Possibly they would be less annoyed about Cadbury appropriating chocolate eggs because for them, chocolate eggs were never a part of Easter at all. We all tend to think of the traditions we grew up with as being timeless, when in fact they are often much newer than we think.
So I think there is a lot of projection going on when stories like this blow up. People focus all their frustrations of a a culture in flux upon one, tiny non-issue. Its particularly counter-productive in this case, because the NT does do so much work to preserve our heritage, and like all charities they need money to do so. At the moment the pot of money available to charities is shrinking, as the number of worthy causes is increasing and this is likely to get worse. Attacking the NT for attempting to make money from Cadbury's is not going to help. Especially when the word Easter was used over and over by both Cadbury's and the NT.
It is a shame that your nephews don't know what Lent is, but if parents want children brought up in a Christian manner, they can not sit back and rely on a school to do all the work for them. This is not a modern phenomenom. Schools cannot (and imo should not) take the place of family. If they don't know the Easter story, why don't you tell them?
I think there is a big difference between teaching children about religion, and telling them that one particular religion is The Truth. The former is appropriate, in my opinion, the latter is not. Is that what you mean by superficial and meaningless?
Sorry to go all pop-psychology, but if you really examine why this issue annoys you so much, is it all possible that the insecurity you are feeling about your own faith might be a factor? Could you be projecting a tiny bit?