There are 5 counters on the top row
kids have to develop in their understanding that if 1 more counter is added to the next row...
they don't really need to go back and count the top 5 again.
But they will.
Time and time again.
Add 2 counters on the next row...and ask, "How many counters do we have now?"
They'll still go back and count the top 5 before giving the new total.
You can add 3, 4, 5, and keep going.
They'll still count the top 5 and add on the new ones.
This all necessary to them developing in number sense.
Eventually - it all falls into place.
But it takes exposure
In different circumstances
With hands on learning
Over and over and over