While there probably isn’t too much competition for this distinction, baby Groot seems quite likely to take the prize for cutest tree-based creature in the history of pop culture. That said, as seen in the Guardians 2 trailer, his childish nature is not always that big a help to his friends. In almost a reversal of the team’s original dynamic – in which Groot was clearly the most powerful member – baby Groot is in some ways a liability, as evidenced by his willingness to push the button that will murder them all in the trailer.
On the other hand though, Star Lord, Rocket, Drax, and Gamora all owe their lives to Groot, and thus are more than obliged to raise baby Groot to adulthood. More importantly, he’s their friend, and they wouldn’t leave a friend behind, even if that friend is a clear and present danger to the success of their missions. Plus, he’s so cute that there’s no way anyone could possibly stay mad at him.