@Lucidas and @Jellycatspyjamas - I think you're both missing the point I was making. I probably didn't explain myself properly.
As adults, most of us apologise for things that we do accidentally, even if they weren't deliberately intended to harm.
For example, I bump into someone and they spill their drink. Did I deliberately intend to bump them? Did I deliberately intend to spill their drink? No. But I still apologise for the outcome because I unintentionally caused it.
In this situation maybe the dad didn't realise that rainbow wotsits were special to the child. He took a crisp, not realising that the child was saving it as special. Apologising for unintentionally causing upset is the right thing to do. You're acknowledging that what you did upset the child, and that wasn't your intention. That's what the apology is for, not whether nicking a crisp is a big deal or not.
Incidentally, I always ask if I can pinch a chip off my child's plate/have a crisp etc. And they always share. I just think it teaches them that everyone deserves respect.
I do get where you're coming from about it not always being right to apologise. Of course, I'm generalising when I say it's the right thing to do.
But I do also think you can apologise to someone, even if you're not at fault. You can be genuinely sorry that you've upset someone, even if you don't think what you did was particularly terrible.
Also, if you upset someone, I don't think it's necessarily your place to decide if they've got a right to be upset.* If you do something innocently, and it upsets them, I don't think it hurts to say "I'm so sorry, I didn't realise that would upset you". It doesn't need to be a big deal, but an apology can mean a lot. And I think its the kind of behaviour which is positive to model to children.
Genuinely, I don't understand what's so hard in just saying sorry. It just seems like common sense to me.
*I am adding a caveat. I'm assuming we're talking about nice, regular folk who you have a healthy relationship with, not hysterical drama queens or narcissists who make everything a problem. Just ignore those dickheads 😅