~~ and I see others doing likewise.

Yesterday, I was at Lowes, buying a pair of safety glasses. Their aisles are wide, and there was no problem. Inventory is placed on shelves from the floor level, on up to above my head.

Book stores tend to have narrow aisles, and my experience has always been that this is to be expected. Excusing oneself is the customary way to ask another shopper to let you pass if the aisle isn't wire enough to simply walk around them.
Only once, many years ago, was a book store ever rude to me. As I was taking a few extra minutes to look through a book I was considering to buy, a loud "This ain't no library, buddy!" rang out from the checkout a few aisles away. Needles to say, I never went back there again.

How your squatting down in the aisle with a small child could pose a fire hazard is beyond me~~ if a fire started in the store, I'm sure you and your child wouldn't keep sitting there, blocking the aisle so that others couldn't get out of the place.

That employee was very rude and out of place, and I would have asked to see a manager, if not right away, after the little girl calmed down in a few minutes waiting just outside the store, perhaps after taking her out into the mall's open area.

It could be lack of training, or just a jerk who shouldn't be interacting with the public at all. You should have seen a manager as soon as the child stopped crying. At the very least, you are owed an apology, and if it were my store, I'd offer a generous discount should you wish to purchase one of those children's books.

You might find that the person who was nasty to you actually was a manager. If this is the case, I would complain higher up [if there's any way to do so,] and take it from there. A girl I used to date worked at Macy's, and she told me her manager was lording himself over every person on the floor, not allowing employees to sit at their stations or go to the bathroom when nature called. I met this man only once, and when I attempted to introduce myself, he refused to shake my hand, and in a curt, unpleasant tone of voice, told me not to interfere with my friend's doing her job. This was enough to make me complain to the store's central office upstairs; I was given a butter-up and sent on my way. A few days later, my friend quit, after having worked there for several years. End of story.

Businesses who treat their customers and employees like this have a tendency to end up in bankruptcy. Many people in upper management cannot see the vast tracts of forest beyond the tree right beside them. They don't seem to realize that if not for the customer, they would be spending alot more time at the unemployment office than managing a department store.
That's my nickel's worth of opinion....