I was looking for a portable MP3 music player for kids that has built-in speakers and came across the GOgroove SonaWAVE 3. It's a small cube that looks kind of like a mini-NAS device. I wanted something inexpensive and luckily Amazon has it on-sale for $20 with free shipping if you have Amazon Prime, or free shipping if you add some fillers to get to $25+ if you don't have Prime membership. That is a very cheap price IMO. I looked on eBay and they were all going for about $31 BIN (Buy-it-now), with an auction that is already $25 with about 2 days remaining (ouch for those bidders). The GOgroove SonaWAVE 3 can accept an SD Card and USB sticks and play MP3 files from them. I play on using an SD Card so that nothing sticks out of the player. BTW Amazon has nice selection of FREE songs for children you can download.
Now I can't vouch for the quality of the GOgroove SonaWAVE 3 since I have not received it, but I will be sure to update this article when I do with some comments regarding its ease-of-use and how well my son (a 23 month-old toddler) likes it. The product has a 5 star rating from 6 reviews, but none of them seem to be from "verified buyers", but at $20 it is not a big risk. The player/speaker is supposed to have a battery life of 3 to 5 hours. We'll see- I will post my findings on my experience with that as well.
[UPDATE] I have received the GOgroove SonaWAVE 3. I must admit it is larger than I had expected despite reading about the dimensions beforehand. It's a sizable cube and a bit bulky, like that of a satellite speaker. My nearly-2-year-old toddler has trouble turning the thing on and off because the switch requires some force using the tip of an index finger in order to move. Sound-wise it is capable of playing quite loud, and music sounded pleasing and detailed. I imagine the GOgroove SonaWAVE 3 would be a good compliment when you are having a picnic at the park or hanging out with a small group of people in your backyard. Battery life was as expected- I had it playing one time for over two hours and it didn't have a hiccup. For a 2 year old, I probably wouldn't recommend this player/speaker, but for kids 4+ the GOgroove SonaWAVE 3 may well be easy to operate.
[UPDATE 2] I've found a MP3 player with built-in speakers that has been working great for my 2 year old toddler. It is the Veho VSS-009-360BT Bluetooth Speaker
. It is light and about 2"x2"x2" in a cylindrical shape. The controls are easy to use and master by my son, and the battery lasts about 4 hours. Like the GOgroove SonaWave 3, you pop in a memory card and it will automatically play the MP3's on it. The Veho VSS-009-360BT uses a MicroSD card, however, while the SonaWave uses the regular size SD card. The only negative I could find is that there doesn't seem to be repeat/loop option, nor does it seem to be able to shuffle songs randomly. Then again I wasn't able to find those two controls for the Gogroove SonaWave 3 either. Another drawback is that the Veho MP3 speaker is more expensive- I was able to get it for $35 from one of the daily deal sites. Then again when you compare that to the $45-ish price points that the defunct Sandisk Sansa Shaker MP3 is going on eBay, it's a bargain. And it has Bluetooth functionality (which I didn't test) to boot.