Try the old games - the reason they are old games (around for many years) is because they are fun and educational and they work. They are also free, can be done in virtually any situation and can be adjusted to suit any starting level. To us they may sound a bit mundane or boring, but we have done our childhood and know these games inside out. Our children are just discovering these games or tricks.
Play:
I SPY - this teaches children to take turns, to listen to others, to keep trying, to recognise LETTER SOUNDS, improves memory (which words have been said), to tolerate failure, improves vocabulary....
SIMON SAYS - this teaches listening, attention span, turn taking, it can be very physical or musical or whatever skill you like could be concentrated upon in the instructions
MEMORY GAME - [memorise all the items on a table, cover them up and remove one, what is missing? This can be done on the move by using a bag, tip out everything except one item and guess what is missing] this teaches concentration and memory
SNAKES AND LADDERS (0r other board games)- this teaches turn taking, adding (and if you count how many squares you went down the snake, you can also do subtracting), persistence....
All of these can be done outdoors. The first three can be played for just a few minutes at a time and are infact much better that way as little and often, produces better learning. For example you are at a playground and the little chap comes over to you after wearing himself out. You play Simon Says and give just 4 instructions to do before he's 'out'. So it is his turn to be Simon and you do the instructions (which are probably the sames ones you've just given him, so remember to vary your own instructions each time you play). He loses interest and goes off to do the slide. On the walk back to the car you play I SPY and have just 2turns each.
Don't expect him to spend 20 mins on something when it is a game of your choosing. But do join him in his games for 20 mins a day, follow his lead, let him dictate what you both do during this quality time. It may be he is digging at a crack in the mud in the garden. Go sit beside him and do it too. If he moves off to push a bike around, pretend you have a bike, mimic him and follow him, if he strikes up a conversation just chat about the stuff he is talking about. Dont bring up why he left the toilet seat up again or what you had planned for next weekend, this is his time and you talk about the here and now and what you are both currently doing. "You are digging that hole. It's getting really big. I bet you could fit a whole dinosaur in there"