Can I please set the record straight in relation to the definition of theft?
Sect 1 Theft Act 1968:
A person commits theft if they;
dishonestly
appropriate
property
belonging to another
with the intention
of permanently depriving them of it
There have been some incorrect views on this thread in relation to what does and doesn't constitute theft (and, incidentally, also about the age of criminal responsibility, and parental responsibility for the actions of minors).
At the point where the OP fed her child the banana, she appropriated it, as she had assumed rights of ownership to consume it. However, it was not dishonestly appropriated.
Dishonesty can be established by observations of the actions of the person, for example, did they conceal it? Pass opportunities to pay etc.
My interpretation of the OP's comment of 'Do you know how much I spend here?' may have been that she was trying to demonstrate that there was no intent to dishonestly deprive, not that she somehow felt entitled to help herself to bananas.
She doesn't state in the OP whether or not she apologised and offered to pay.
Although I may be a bit soft. I'm sure lots of shoplifters come out with these sorts of lines.