Hi -- I've taken trains with my kids, 13, 16 & 18 (sometimes we get a room sometimew we don't). Definitely take DVD player, CD player, cards, books if your child needs to be occupied. Mine can only look out the window for so long. Also, bring plenty of batteries -- while you may luck out and get a seat with an electrical outlet or able to charge up in the lounge or dome car, this is a long shot and you may have to rely soley on batteries (same thing for cell phone if you need to have it with you).
K
K