How would the acceleration of a chain of three shopping carts compare with the acceleration of a single cart if the same force acted on both?

F = ma

Let the mass of the 3 carts be 3m.

F = (3m)a 

a = F/(3m)(1)

Now if the same force F is acted upon by a single cart, let the mass, be m.

F = ma

a = F/m(2)

From equations (1) and (2) we can see the that the acceleration on the 3 carts is less than that on a single cart by (1/3).

That's if the each cart has the same mass.