There seems to be a consensus that the OP was guilty of negligence - but I'm not sure that is the case.
As someone mentioned previously, the case law on negligence requires there to be a duty of care on person A in relation to person B - the negligence being that that duty was not met in a specific circumstance. The classic case was Donoghue v Stevenson 1932 where a woman drank a bottle of ginger beer which her friend had bought her in a cafe. Unfortunately, the bottle contained the decomposing corpse of a snail (yuck!), and the woman sued the drink manufacturer on the grounds that they had been negligent when they produced the beer. And she won.
In his summing up, the Judge (Lord Atkin) provided what is still the basis of the common law duty of care:
The rule that you are to love your neighbour becomes in law, you must not injure your neighbour; and the lawyer?s question, ?Who is my neighbour?? receives a restricted reply. [?] The answer seems to be ? persons, who are so closely and directly affected by my act that I ought reasonably to have them in contemplation as being so affected when I am directing my mind to the acts or omissions which are called in question.
In this case, would it be reasonable for the OP to think about the potential effect on Audi woman contemplation about her actions? It was raining, there was a sick and distressed child and the trolley only moved because the Aldi car park is on a slope. If anything, a court might argue that any accusation of negligence might better be levelled against Aldi.
And if you think I?ve been making this up, have a look at Wikipedia: en.wikipedia.org/wiki/Donoghue_v_Stevenson