Welcome to the board!A few suggestions-Don't check anything you will need or that is breakable. Each passenger can take 2 carry on bags, so do an overnight bag for each of you with your essentials. On the TE, they can be stored a few steps from the family bedroom in the luggage rack. Surfliners also allow carry-on bags. Carry-on baggage is limited to 28" x 22" x 11" on Pacific Surfliner trains. On the Texas Eagle, they can be slightly larger, 28" x 22" x 14". Each passenger is also allowed 3 checked bags-36" x 36" x 36", up 50 lbs each-all at no charge.
You may want to bring a laptop & dvds & headphones, or some games/toys or cards in case the kids get bored.
Have a great time!