I think her main grievance is:

1) you are not a child

2) yet, you're suddenly start being addressed as a child

3) you get used to it (even if you protest at first; or maybe the silent majority doesn't mind?)

4) because of 2&3, with time, you became infantile (which, certainly, could be an exaggeration)

5) apparently, this technique works quite well for "customer retention"--you feel "safe", for everything that is presented to you is cosy, cartoonish, kid-oriented staff