Just to confuse the issue, I would go for the full grown rooster! haha.
But just to check, how old are your birds? If they are laying, then they are old enough for a rooster, and a rooster is the easiest add to make. They will all be in love with him by morning! And when you get an older rooster, if he is pretty close to a year old, he is going to act like he is going to act, for the most part. I think you would be more apt to get a pleasant rooster from a multi- generational flock. There are lots of cases of home raised roosters starting out as pets and becoming the very devil.
However, roosters really change the dynamics of the flock. He will look to you, the hens will look to him. Generally speaking, he will put himself between you and the hens. Then hens will become less pet like, and more flock like with a rooster.
And considering the size of the rooster's brain, and add in a good dose of hormones, well, one needs to always be aware of a rooster. If your children are very young, I would wait until they are older. Lots of roosters have ruined the whole chicken experience for kids.
And last but not least, if you get a rooster, you must be prepared to cull or remove him from a flock, if he does not work out, that might be nearly immediately or it might be years down the road. But one cannot wish a rooster nice, and nearly all of us have tried. He may be an sweetheart from the get go, roosters are just a crap shoot, and you need to be prepared.
Mrs K