What are 4 x 4 and 6 x 6 puzzles?

Small grids for children and beginners: 4 x 4 uses the numbers 1 to 4 in four 2 x 2 boxes, 6 x 6 uses 1 to 6 in six 2 x 3 boxes. The kids type starts with 4 x 4 and moves on to 6 x 6.