I just thought I'd share where I got mp3s for the primary song CDs (don't worry, nothing illegal).
The LDS website has suggested mp3s here, but I was so excited to find some other options too.
1) If the Savior Stood Beside Me--here is a free mp3 that's gorgeous from Sally Deford's Website. I use the one from Angie Jack. Just a note on the church website version: the kids sing the wrong word on the 2nd verse. Just another reason to use the Angie Jack version.
2) Audio from General Conference children choirs!
I was thrilled to find these. Just search for whatever song you want. "My Heavenly Father Loves Me" is under the name Primary Song Medley (yes, with I Know My Father Lives)
I like the children choir versions better than the ones suggested in the primary program links.
3) You can beg people from Youtube for the right to use their audio. I had little luck with this route, but I found lots of versions of songs I'd love to use if I had permission.