What to do? What to do?

Old Sophie lives all alone and yearns for someone to talk to. Her wish comes true one day when she hears some birds sing to her. “Nice lady, sweet lady,” they seem to say. Sophie is so delighted that she bakes her most delicious bread for them. But before long, their sweet twitters and tweets turn into greedy squawks and screeches. Soon, Sophie is weary of kneading, weary of baking, and very weary of birds. What to do? What to do? This is the dilema I face: I know how to play with my children at first but then after a while I don't get sick of them, I just don't know What to do? What to do? with them.
How do you play with a 4 year old. Anyone? When they're little it's helping them walk, teaching them words, playing with their tummies and just kinda following them around.
With my 4 year old. I'm great with park days, play dates, teaching him how to write his letters, reading to him, playing games and doing puzzles. When it come to pretend sword fighting, bad guys and Legos, I'm so totally clueless! Keegan asked me if I would play Legos with him earlier today and I said "sure". They were the Mega Legos and he just built a little tower like thing and tried to set it up on the floor. I said "how about you stick it on the wagon (that was made for the mega legos) so they're not directly on the ground when the flood comes"? He looked at me funny and my husband shot me a look like what in the world? What to do? What to do? How in the world do you play with a 4 year old? Please, I can seriously use all the comments and imputs that you have.