One of the biggest emotional punches in the original Guardians of the Galaxy was when Groot sacrificed himself to save the team, uttering his immortal line, "We are Groot." The sadness turned to joy, however, when it was discovered that Groot had survived as a tiny sapling — one who was adorable and enjoyed dancing to the Jackson 5. And fans might be surprised by just how old Baby Groot is in Guardians of the Galaxy 2, as the little fella is now pretty grown up compared to his last appearance.
In the new movie, the character's name is a bit of a misnomer. While he was definitely a baby at the end of Guardians 1, he's a bit bigger and more capable in the sequel. He's much more stout, he's no longer confined to a pot, and he can walk and even talk in a higher-pitched voice (three guesses as to what he says). The name "Toddler Groot" probably would have been more appropriate, but it admittedly doesn't have the same ring to it as Baby Groot, so there you go. And if you've seen the trailers and marketing materials for the new movie, then you probably have a pretty good idea of what to expect from this new incarnation of the wooden alien as he tries to relearn how to be Groot.
First and foremost, he's adorable, let's get that right out of the way. He's also an entirely different character than the Groot of the first film. The original Groot was the most physically imposing member of the team, but Baby Groot is the least intimidating. While Groot was Rocket's protector in the original film, those roles have now largely been reversed. But even though Baby Groot is small and cute, don't let that lull you into a false sense of security — he can still handle himself in a fight. Also, the dance moves of Baby Groot are far superior to those of Adult Groot, possibly even besting Sapling Groot's moves in the first film.
If there's a downside to Baby Groot in the film, however, it's this: He's not really in it a ton. This could be seen as good in a way, as it prevents overexposure and makes the scenes he is in feel more special, but it could also come off as a big letdown if he's the main reason you're going to see the movie.
At the end of the day, Baby Groot makes the Guardians feel like a different team than Adult Groot did, and the version of the team that you like best will likely come down to your personal preference.