I have to stick out my tongue instead of flipping the bird in traffic, because it’s guaranteed I will see that person again. 
All of the above.
I love re-reading all the children’s books I enjoyed when I was small. And I still collect my favourites now, buying them on abebooks and amazon.
Also, I do not have children. lol
If I pass someone walking a dog, I always say, “Hey dog!”
I love stuffed animals. I restrain myself from buying them almost all the time, so I only have a few, but I love them. I have a special stuffed monkey who sleeps with me, and a stuffed panda who meditates with me.
In fact, toys and toy stores are generally great.
A less wonderful teenage part of me: I care too much what everyone thinks about my childish behavior. An example - a renaissance fair, one I’d driven three hours to attend, had a line for an elephant ride. I’d never ridden an elephant, but it looked like only kids and parents were in line. I wanted to ride that elephant so damn bad, but I couldn’t bring myself to do it. 
I was over 30 before I had even heard of Toys ‘R’ Us, but I made up for lost time once I had discovered them. Even if I had no money, I loved browsing.
Now they are going away, and I am so sad.
Meh. TRU hasn’t been the same since switching from aisles to islands. I probably haven’t been in the local store more than a dozen times since they adopted this configuration.
That’s true for me too. However, when the attraction is totally irresistible, I just don’t care, I push in front of the kids and have a blast. The embarrassment comes later, when reviewing the pictures.
I was about 25 when I decided trying out every swing I saw was too weird. That was also the time when playgrounds started installing information boards indicating the permitted age range of users. Breaking rules is not my style, but I still think this is unfair. Height and weight ranges would make more sense.
I share pretty much all childish behaviours mentioned in this thread, but I don’t claim to be completely mentally all right. 
I can sleep without this, but not nearly as well as with. Not sure what I’ll do when it finally falls apart, but it’s holding up surprisingly well after 22 years.
Me too! I have a huge purple Harmony Care Bear that’s just the right size for cuddling. I have a hard time sleeping without it.
It would be easier to single out the few ways I am an adult-like.
I am adult-sized.
Sense of wonder most prominently-if you were to follow me around all day long you’d see me constantly looking up at the wonders of the sky (followed a Mississippi Kite today at a stop light while it soared all over the place in the clouds above), or chuckling quietly at the antics of the 4 y/o at the grocery store, or just grinning like a silly person at the sheer wonder of it all, of being alive. Can shed tears (of happiness, or of wonder) at the drop of a hat.
Honest and trusting. Some say too much, I say it’s too rewarding to quit.
Very silly and imaginative. My bed is sometimes perfect for pretending to be a jellyfish. I can’t say I’m feeling sluggish without making antennae. I recently started a medication that makes me prone to sudden drowsiness so I invented the concept of sleep gnomes, mechanical critters that come and carry me away and tinker with my brain while I’m napping so I can wake up with a finely tuned brain. I can’t even stand the fact that the new Finding Dory movie has an octopus character. I thrash and wriggle in excitement just thinking about it.
I can’t wait to have kids to play with. My husband says he can’t wait until our future kids get old enough to realize I wasn’t just patronizing them that whole time… I really am this silly.