Perhaps you could explain it like this.
Let’s say we put 4 dogs in a pen, another 4 dogs in another pen, and so on. Let’s say we have 20 dogs, 4 to a pen. So we end up with 5 pens. Now take away a pen. How many pens left? 4, of course. Now we take another pen away, leaving 3. That means we have 12 dogs, because there are still 4 dogs in a pen and 3 pens contain 3×4=12 dogs. Take 2 more pens away, so there’s one pen remaining, containing 4 dogs. How many dogs do we have if we remove the last pen? We have no pens and there are 4 dogs in a pen so we have 0×4 dogs, which is no dogs at all and that shows that 0×4 dogs=0 dogs.