While we all need to grow up and accept responsibilities, it can be okay to try to have some fun now and again. For example, I think it's fine for adult men to collect remote control cars and play video games, within reason. Just as it's okay for women to collect knick knacks, dolls and things. Also, the wonder with which a child observes the world is something we can all aspire to emulate. However, one thing that doesn't look good on any adult is having a temper tantrum. So, there are certain ways it's okay to have childlike behavior, but emotionally, it's not okay.
If you work with children and it is ok to play with them, then yes. Connect with your inner child. There are times when an adult should be an adult and times when an adult can act like a child again. For instance, it is not a good idea to act like a child in a business meeting. At an amusement park such as Disney World, it's A-Ok! Just don't forget about your other responsibilities.
Yes, it is proper for adults to act like children, because there is no reason for adults not to enjoy life like children do. If an adult would like to enjoy a water slide, there is no reason for them not to. If an adult wants to sit and have a good cry, there is no reason not to do that too. Adults need to be responsible, but childish behavior is fine in some contexts.
I think it is perfectly fine for adults to act like children, and is completely proper is some situations. It is probably not a good idea for an adult to act like a child at work or church. It is fine though, if the adult is at Disneyland or something!
I do not believe it is appropriate for adults to act like children. I believe it is a grave injustice if an adult feels that poor or improper behavior is okay. Acting like a child, as an adult, only shows the immaturity of the adult, which could potentially ruin their life.
It is not proper for adults to act like children. They should act like adults, that is where they get the name afterall. Adults need to behave in a way that children can look up to and learn by example from. Adults are important in society because they are the ones who make all the difference.