What a great word.
My youngest daughter and I were at the park yesterday. She began by swinging high on the swing, with her head lolled back and a big grin on her face. She then slid down a large yellow twisty slide made of plastic. The moment she was at the bottom, I heard "again". I popped her back up as there was no way for a toddler to climb up herself. "Again." I popped her back up...again...popped up...again...popped up...again...by eleven agains, I convinced her to go back on the swing for a while so mommy could rest.
It is no wonder again is one of the first words kids learn to say.