My main critique is that the shading appears pretty grainy at 1x. You might want to try studying other styles of colouring to find a way that you might make them appear more vibrant and smooth, because the shading at the moment sorta sucks the life out of them and makes them look like wrinkly old turtles.
They are still cute! Another thing would be that the feet and hands are very square and that doesn't quite balance with the rounded head.