If a Smart Playlist Doesn’t Appear on Your iPhone After Syncing
Let’s say you’ve created a smart playlist in iTunes that has only one simple rule: Genre is Children.

After setting up your iPhone to sync to iTunes, you might notice that the songs in that playlist appear in the Artists, Albums, Genres and Songs tabs in the iPod app on your iPhone, but that specific playlist, Children, doesn’t appear in the Playlists tab.
This problem seems to happen if your smart playlist only uses a single, Genre rule. A smart playlist that’s created with other rules seems to not have the same issue.

The solution, or rather, workaround, is to add an additional rule to your Genre-only Smart Playlists. This rule can be of any type, but what’s most convenient in my case is to append the Playlist is Music rule.

Syncing Genre-only playlists with the additional Playlist is Music rule will now ensure that these playlists correctly appear in the Playlists tab in the iPod app on your iPhone.