The thing I’ve read about earbuds is that it has nothing to do with the volume. It’s how close they are. Our ears are designed to catch sounds from out in the environment and direct them inside, not have them pumped straight in.
There are two options.
From the iTunes help manuals:
- To have all songs and videos always play at the same volume level, choose Edit > Preferences, click Playback, and then select Sound Check.’
- Some songs or videos in your iTunes library may be louder or quieter than average. To adjust the volume of a particular song or video, select it, choose File > Get Info, click Options, and then drag the Volume Adjustment slider left or right. iTunes will use this setting each time the song or video plays.
I found option 1 didn’t work all that well, because it doesn’t really help must with unusually loud peaks in the middle of tunes. So I adjust the volumes indicidually (or in groups) using method two. I’ve found that volume tends to be pretty consistent for all tunes inported from a single CD, so I select all songs from a CD after inporting them and change the volume setting as a group.
Oh yes, and absolutely set the volume limit option on the iPod itself. Apple, IIRC, was forced to install that control as the result of a number of lawsuits charging ear damage from unts playing at too loud a volume.
Someone’s already mentioned Barenaked Ladies, but not that they have a children’s album out, Snacktime. It’s good and funny, even for adults. Supervenusfreak had it on pretty constant repeat for about a week when it came out.
To add to the above (I went looking for YouTube clips and lost my five minute edit window), their songs are pretty smart and witty, too. Check out the “789” clip on the linked page.
Well, you can’t go wrong with a little Eminem.
Oh, wait. Yes you can.
Anyway, at that age, my daughter was into the Beatles, Fountains of Wayne, The Jayhawks, and Avril Levigne. What can I say - the kid has good taste.
But the common denominator is that all this music is very melodic. I’d look for music with strong melodies.
I think kids like The Beach Boys quite a bit. Also, lots of the more upbeat 50’s/60’s stuff like Johnny B. Goode and Whole Lotta Shakin’ Goin On. Some Elvis would be good too.
When my own angel was five he thought Spinal Tap was real, so what about Big Bottom or Sex Farm? Okay, Tonight I’m Gonna Rock You and Stonehenge might be better.
My boys are around that age. As you mentioned, TMBG in general.
They also likeRalph’s World quite a bit. As well as For the Kids
For singles we play:
The old Spiderman cartoon theme
The Monster Mash
Love Potion #9 by The Searchers
The Letter by The Boxtops
We also play a few soundtracks:
The Sound of Music
Chitty Chitty Bang Bang
As others have mentioned, kids love just about anything that they can listen enough to get used to. You can include any music that you already own and she’ll dig it – plus it is a nice thing to share.
You all are the best, I have two CD’s worth of *kind * rock to bring over tomorrow morning for the kid. I swear that he’s going to love this stuff.
And maybe I’ll keep a little for myself. Maybe just a little. Don’t tell the metalheads. 
We’ll let you keep this one for yourself 