Remember those mittens? Here's a good example of an older kid who still uses his hands as if he's wearing mittens. He uses his four fingers together to pick up a small checker, rather than using a more precise pincer grasp with the index finger and thumb. That's what is called poor differentiation of the two sides of the hand and of the fingers. The thumb, rather than forming a nice rounded space between it and the index finger, pulls in towards the palm. That indicates underdevelopment of the thumb's webspace. This kiddo needs more proprioceptive input to increase that internal awareness of each finger and its movement and position in space.
Another activity that provides proprioceptive input to the fingers is playing with a geoboard. The board has a grid of pegs on which the child can stretch rubber bands to make shapes and designs. Stretching the rubber bands usually encourages the child to isolate the index and middle finger, or just the index finger alone. The stretch provides traction to those fingers, which provides proprioceptive input.
Using a geoboard does require a moderate degree of coordination and motor planning, but if the child is having difficulty, you can help stabilize the band on a peg or two to prevent them from slipping off.
The geoboard also provides reinforcement of shapes and colors. You can ask the child to copy your shape, or you can ask if he can make a yellow square, green triangle, etc. For more advanced play, you can even print diagrams of the board and see if the child can copy the design from the printed example.
Geoboards are available at educational supply stores.