Playing Trains With a 2 Year Old

Isaac loves to play trains. If you let him down in the basement where the wooden train set is by himself, then every few minutes he will come to the foot of the stairs and yell up "Dada you comin to play trains." We had a little problem a couple of days ago. We could not find the black engine. The black engine is definitely Isaac's favorite. Interestingly he was perfectly willing to play by himself with the other trains while he let me look all over the house for the black engine. The funniest thing about playing trains with Isaac is that he is very picky about what he lets you play with. The train cars consist of a black engine, a blue car, a yellow car and a green car. Isaac always plays with the blue car and the black engine. He does not even want the yellow and green cars in the same vicinity as the blue and black ones. He will pick up the blue and black ones and move to a different part of the track if you come to close. Also I stopped playing with the trains on the track and started playing with a tennis ball. He promptly took the tennis ball from me and hid it behind a filing cabinet. Then came back and says "Dada play with trains." He is lots of fun.
-Tim