Branch was definitely behaving like an adult who is just focused on his work & 'things to do' & lost his Joy of life. And He was the only one predicting danger & warning the others against it telling them that 'The Loudest & Craziest Party they wanted to throw was not a good idea'. He also told Poppy to be quiet in the Bunker Scene you can see in the header ( adults are usually the ones who tell Kids to be quiet when they talk too much, right? ). 

The rest of the Snack Pack behaved more like children who just wanted to have fun & didn't listen to any warnings 'not to throw the Biggest Party' ( but that can be understood - If Branch was telling them that 'The Bergens are coming Since 20 Years - & nothing happened, they felt safe & couldn't know that some Bergen would appear now ).

Poppy was also behaving quite childlish at the beginning of the movie ( although she was an adult, about 20 years old ). She was only thinking about nice things, scrapbooking, singing, dancing,  & hugging, living in her Happy 'Cupcakes & Rainbows' world till she faced real danger:  Chef Kidnapping Her Friends . I admire her for Bravery because she wanted to go & save them Alone - but have you noticed that she went for the Rescue Mission kind of 'unprepared' - not taking any food or Absolutely ANYTHING with her? ( Branch thought about that, he was prepared, he followed her with a backpack - he even took the Sleeping bags for Them Both! ).

The Pink Troll Princess although brave, optimistic & adorable had No Plan how to save her friends! - she only wanted to Save Them but didn't think of Any Strategy how she could do that. And she was 'loud' talking all the time & singing even when Branch asked for some silence, which he could find annoying at that stage ( Yes, her song was nice & the 'Sound of Silence scene' was Funny... - but I kind of understood Branch when he took her ukulele away - He asked for silence & she didn't listen... - but I think he shouldn't have burnt it anyway. Just taking it away from her to have some peace & quiet would be enough in my opinion - but I guess the 'throwing Poppy's ukulele into the fire scene' was also to be kind of 'funny' because the Face Poppy made Then was Priceless! ). 

She gave the ukulele to Branch herself when he asked her 'May I?' cause she probably thought that he wanted to play it as well - so she got as surprised as This when he threw it into the fire: 

... & he looked 'Happy that he will have some silence at last' ( if we could use the word 'happy' talking about him as early as that ). I'm also sure that Branch was the one who made that bonfire cause he had all the 'survival skills' - although that scene wasn't showed in a movie. 

And one last thing to finish this part: Just look at the header picture again... - Can you see that? - Poppy rised her hand to let Branch know that she wanted to say something after he made her quiet a few times ( so she looked kind of like a 'schoolgirl' then - cause kids rise their hands At School to inform the teacher that 'they have something to say'! 😁 )