i think it probably depends on where you are traveling. I have had excellent experiences outside the Northeast Corridor, and mediocre ones within it. (I travel from southwest of DC to northeast of NYC). I've never checked a bag, and what I do is have the person dropping me off help me onto the train, and I stow the luggage while they are watching/corralling/holding the child. i try my hardest to have a trip where I don't have to change trains (and in fact, re-routed my son and I to a city an hour east of our home when our last trip got screwed up and we would have had to change trains otherwise). I've also never had a problem storing my luggage--though I do try to get on in smaller cities before the train would have really filled up. If you are polite about asking someone to move so your whole family can sit together, people are generally accommodating as well.
Our last trip, we got into the station after midnight due to terrible delays, and my DP was late to pick us up (that was the trip where we were re-routed) and the conductors not only unloaded all of our bags for me, they then drove us and the stuff in their golf cart to the front of the station while my son slept in my arms. But, I do recommend a luggage cart, a sling and no stroller. And, be ready to tip a porter for assisting you. Bring new toys that are a surprise, and be ready to read tons of books. I have found that the other passengers are totally understanding of grumpy and/or loud children as long as the parent is attempting to engage them and is remaining calm and happy in the process.
