I have a 21 month old DS, and am getting to this point also- his attention span is teeny tiny, and it is getting more difficult to entertain him, particularly in the cooler weather. When it is warmer we try and spend a lot of time outside.

DS tends to wake up about 8:30am, and has breakfast straight away. I find that the mornings are best for him, so that's when I try and do activities that need some concentration like drawing, or playdough. 3 days a week I go to the gym for an hour in the morning so he gets an hour of interaction with other kids, and 1 morning a week we have playgroup- the most fantastic thing ever invented!

Playtime on his own and cleaning up time for me generally happens before lunch (so around 11-12), then then has lunch, and a sleep, and wakes up late afternoon. I find this is the most difficult part of the day- so generally try and go outside for a walk, or let him have extended playtime in the bath.

I don't know your situation, but would something like playgroup or occasional child care give him something a bit different?