Audio for kids

My kids have started using their tablets (in this case Kindle Fire) for everything, including music. Ordinarily I wouldn't get into their business (at least, this business), but since they've started to discover that Dad has some good tunes, I think they should be able to hear them on at least decent gear. Headphones I've got covered, but I'd like recommendations on headphone amps or amp/DAC combinations for pre-teens.
I was going to say that a 10 year old kid doesn't need a dac, but then again, I remember being enthralled by my uncle's JBL Paragon/Mac system when I was no older than that. If you have USB, I think the Audioengine is a really nice little piece. No menus, just a volume knob and an on/off switch. Sounds amazingly better than the computer jack.
The Audioengine D1 recommendation from Chayro is a good one. It has USB and optical inputs, the optical input made it attractive to me for connecting to an Airport Express for streaming to a small workshop system.

If you need a coax connection rather than optical the Nuforce Icon UDAC or UDAC2 have that plus USB in a small, inexpensive package.
vintage receiver, descent working player and boston bookshelf speakers put together for less than $100 will to the trick.
Yes, I forgot that the D1 has optical, but it needs to be powered by USB.
How about one of the new NAD D3020 int amps? This baby is sweet and has everything I think you and the kids would need.
Chayro - Yes, you're right, if you're using the optical port you need to provide power through the USB port but that can be done with any 5V USB phone charger or other 5V source.
Take a look at Schiit

I have their Bifrost DAC and it is very well made and performs to a very high level when you use the right interconnects and power cables.

Their entry level is $99 for headphone amp and $99 for simple dac