I agree with all of you. All of those scenes were very serious and emotional, no doubt. Some of my choices you've already mentioned, but I'll add what I can. The most dramatic moments I can think of off the top of my head that haven't been specifically mentioned are:
1. Littlefoot's mother dying in front of his eyes and him having to leave her and go on his own. No child should go through that. (The Land Before Time)
2. Littlefoot's friends don't want him to leave them and live with his father, but because they care so much, they only want him to be happy, so although they don't specifically tell him to go, they make it clear that they will be fine with whatever he chooses, which takes place during the song "Bestest Friends." (The Land Before Time X: The Great Longneck Migration)
3. The look on Chomper's face when, because he feels alone and wants friends near him, he asks his friends to stay at his home, but the others know that they must be with their families, and therefore turn him down. While I know the others did the right thing, I felt so bad for Chomper I wanted to cry. He had had a taste of happiness, then it was taken away so quickly. (The Land Before Time V: The Mysterious Island)
4. When Ruby sees another family playing together and gets really homesick. She remembers all the good time she had with them and the song "Remembering" really adds to the sad feeling of her missing her family. She needed her friends the most right then, but they wouldn't play with her. They were preparing a surprise for her, but just being with her was the best thing they could have done. (The Star Day Celebration)
5. When Chomper nearly drowns and it takes several of the others to help him since he was tied up and couldn't move. He must have been terrified. He was underwater for so long that I was afraid he had inhaled in a bunch of water and when he surfaced he wouldn't be able to breathe. He ended up alright, but it was so close. (The Missing Fast Water Adventure)
Those are the five most dramatic scenes that I can think of on the spot. I hope that that was a little helpful.