How do I create one picture that has 2 different pictures side by side on a MAC?

I have a mac computer and am still getting used to it. I have 2 pictures of me and my son, one from last July, one from this July. I would like to put them into one picture together. How would I do that on a Mac. I have iphoto or would I use the keynote or pages programs. Please let me know, thanks!