The problems with wearing an IEM while running is that the isolation might be dangerous, especially if you are running near traffic, and the the sound of your feet hitting the pavement will reverberate in your ears(I guess due to bone conduction?)
Perhaps you should consider getting some earbuds with ear hooks that don't isolate. Many complain these don't have enough bass, but I find boosting the bass around 8db with the player's equalizer compensates just fine for that. Some cheap options are the Panasonic RP-HS33 and JVC HA-EB75. Imo these are decent enough to use while exercising. The RP-HS33 sounds a bit better, but may be too large for small ears. The HA-EB75 is adjustable, however it might still be too large for very small ears. The ear hooks on the HA-EB75 are softer and more comfortable than those on the RP-HS33. There are also some expensive Sennheiser ones that I haven't tried yet, as I find these much cheaper ones to be good enough for use while exercising when I need to hear my surroundings. JVC makes some IEMs with ear hooks if you need isolation while working out, and regular IEMs fall out due to perspiration. If you don't have a problem with IEMs falling out, you could try the low priced JVC Riptidz which is sweatproof IEMs. It sounds quite decent considering the price, as does most of JVCs low priced earphones and headphones.