Going by Train?
Unless you appreciate the fact that babies and toddlers are very special people with very special requirements, you are in for a lot of trouble if you attempt a train trip with them. Planning should be done well in advance.
Take only what you must
You will need to make your train reservations early. Select the first or middle of the week for traveling. Stay off trains on week ends or holidays. Travel then is like a bargain-counter rush.
Travel arrangements of any kind are hard to make nowadays. Railroads are geared to military needs and civilians take what is left over.
If you are going on a very long trip, try by all means to arrange for a stop-over or two with relatives or friends. It will give you a chance to rest and get things in order again.