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.