Plot
Every year, as the warm season approaches, a tree in the Great Valley blooms with pink flowers. These "treesweets" are viewed as a delicacy by the dinosaurs. However, because of the tastiness of the sweets, and due to the fact that there seems to only be one such tree in the valley, there is hardly enough for every dinosaur. Because of this, none of them may eat the treesweets until "Nibbling Day", when they reach the "peak of their tastiness". Littlefoot and his friends Ducky, Petrie and Spike wait to eat the first treesweets of the season. Ducky is about to take one, but Littlefoot tells her to stop, reminding them that "Nibbling Day" has not arrived yet. This does not stop Petrie from attempting to take a treesweet, until Cera's father, emerges and states how everyone has waited all year to taste the treesweets. Cera later boastfully reminds the group that she is the one who is supposed to eat the first treesweet, having been the one who found the treesweet-tree in the first place. However, it was Littlefoot who first found it. Cera also teases Littlefoot for being too little to reach the treesweets, offending him.
Meanwhile, Mr. Threehorn is visited by an old friend, a female threehorn named Tria. Topps promises Tria the first treesweet of the season, and Cera becomes jealous. Cera refuses to make friends with Tria and dismisses her. In addition, Cera becomes violent toward her friends when they make any references involving Tria. Littlefoot wanders off and sulks alone about how "little" he is. Returning to the tree, he climbs the cliff next to it and tries to prove that he can reach the treesweets himself. While doing this, he accidentally slips and falls through the tree, knocking down every single treesweet. Distraught, Littlefoot faints in dismay. After waking up, he finds himself surrounded by "tinysauruses," miniature longnecks. They have eaten all the treesweets and run away once Littlefoot starts screaming in fear.
Noticing that every treesweet is gone, everyone suspects that Littlefoot is responsible. Fearing he will be banished from the valley, Littlefoot makes a parish truth and blames nearly everything that happened on the tinysauruses. At first, everyone laughs at him, but after finding teeth-marks on an eaten treesweet that are too small for Littlefoot to have made, he is believed. Everyone begins looking for the tinysauruses, thinking of them as pests and preparing to drive them out of the valley. While searching the valley, Littlefoot falls down a pothole and finds where the tinysauruses are hiding. At first, Littlefoot is afraid of them and flees deeper into the cave, but he soon finds them to be nice and befriends them. Upon hearing how difficult it is for the tinysauruses to find food, Littlefoot promises to help bring them as much food as he can every night.
Littlefoot's friends soon find him while he is bringing food to the tinysauruses. They also fall in the pothole and, upon meeting the tinysauruses, agree not to tell the adults. Many tinysauruses in the colony feel that their leader, Big Daddy, bosses them around too much, though he is only looking out for them. Big Daddy distrusts the Great Valley's larger dinosaurs. He thinks they believe that "because they're bigger, it makes them seem more important". By morning, Cera decides to be friends with Tria.
When sneaking off to see the tinysauruses the following night, Littlefoot and his friends are discovered by Topps, who is on guard duty and sends them home. Afterwards, he meets up with Tria and they spot two tinysauruses, Lizzie and Skitter, who have been waiting for food. A chase ensues that ends when Topps and Tria, who is trying to stop him, finds the tinysaurus colony. Topps gathers the other adults to let them know that he has found the tinysauruses. As the grown-ups prepare to block the caverns, Littlefoot stops them and admits what actually happened with the treesweets that he first accidentally knocked them off the tree. The adults forgive him and decide to leaving the tinysauruses alone. But the tinysauruses' cave then collapses.
The tinysauruses escape into the Mysterious Beyond, where they encounter a pair of Utahraptors who chase them back into the Great Valley. Upon hearing that Littlefoot initially blamed everything on the tinysauruses, Littlefoot's friends become upset with him. Angry at his friends' rejection, Littlefoot decides to set things right on his own. Meanwhile, Cera apologizes to Tria about Topps being hard on her when she tried to stop him from hunting the tinysauruses down. Meanwhile, Petrie, Ducky, and Spike feel remorseful for making Littlefoot leave. With Cera's help, they all try to find Littlefoot but mistake the sharpteeth for Littlefoot, and the two carnivores chase them through the Great Valley. Just as Ducky is about to be eaten, Littlefoot saves her. Topps and Tria also appear. The tinysauruses then come to the children's aid and fight the carnivores. The grown-ups of the valley reach the group and drive the sharpteeth back into the Mysterious Beyond through the same hole, which they cover up with a boulder to prevent them from coming back.
With everything sorted out and friendships repaired, the tinysauruses then become residents of the valley. When Nibbling Day comes, Littlefoot manages to reach the treesweets by himself. All the dinosaurs share the tree sweets, learning how even small things can make a big difference.
