If I was invited to a coworker's party for her son, and I didn't attend, should I give a gift anyway?

Please read the entire narrative, as there are more details in the last paragraph:

I am not that friendly with my coworker, outside of work. She invited me to her son’s 3rd birthday party, along with a bunch of other coworkers. I did not attend and am wondering if I should give him a check anyway (I was going to give a check if I did attend, I didn’t buy a present).

(I was actually going to ask Fluther a question regarding this invitation but did not. I told her and my other work friends that the same day as the party, we had some friends coming from across the country and it was going to be hard to get my daughter out of the lake (lake we live on and swim in). The girl who invited us said “Oh, it’s ok if you can’t make it.” I told her I was going to try my best, and she seemed to be encouraging me not to come, which I kind of found insulting. I was going to ask Fluther if she was being nice by letting me know not to feel bad if we couldnt’ make it, or if it was an insult. So she did already know that the chances were we were not going to make it)