I watched 4 small children, ages around 5 to 7, try to play Blokus Trigon today. I honestly thought they should be able to do it.
But no. While some of them at least grasped the rules, none of them exhibited any planning. They picked up random pieces to put down. Some of the time they put them on random places on the board until they finally played something legal by accident. Often they put the pieces onto the board but not into the grid, so that the piece was sticking out in a random direction.
One of them took about two minutes for each move. Looked at her pile of pieces. Looked at the board. Looked at her pile of pieces. Picked one up. Put it back down. Repeat for two minutes.
Also, Tal and I played Boggle earlier in the week.