It for sure can work. Jackson grew up with my little sister (who was around 7 or 8 months old when I brought 9 week old Jackson home). My little brother as well, who is now 10. So he was older when I brought Jackson home but still young (5).
Rules and boundaries had to be set early on. I never left them together unsupervised without me (I didn't trust my parents to watch the 2 of them either, lol). It was constant in the beginning though -- when they both were younger. A puppy and a young one can be difficult. They're both into *everything*. So I have to say it was easier on me since she wasn't my kid. I could send her upstairs to be with mom when I felt the pup had too much
LOL...
Now that Emma, my sister, is almost 6, it's really cool to see their relationship. They literally grew up together. They're both very protective of each other as well. If my step-dad leaves a door open, Emma is the first to scold her daddy. She makes sure nobody gives him any table scraps that are unhealthy for him. She does tricks with him that I've taught him, and he tries so hard to understand what she's asking of him. He knows what time she gets off the bus EVERY day and wants to go to the end of the driveway to pick her up. She has learned a lot about animals and dogs because of him, and compassion and respect that it takes to live with one.
Here she was at 3years old with him:
But definitely give the puppy a space to go to call it's own, like an ex-pen. I agree with everything bjh posted.
It is not something that will be "easy" especially in the beginning. A puppy is like having a young toddler. But I think in the end it's worth it.
I SHOULD add that Jackson is also a bit larger. He was already 5lbs at 9 weeks old and is now 17lbs.