If you are primary looking for layers, look at Isa Browns they lay approx 300 eggs a year, are docile, friendly, great with kids. Another one is an Australorp cross layer, much the same as the Isa Browns in temperament and egg laying just black. Unfortunately due to them laying so many eggs per year it can take it out of them and they don’t live as long as heritage type breeds.
I would stay away from leghorns they are flighty, not as docile or friendly but depends on your needs and wants.
For heritage breeds well there is lots of choice and I suggest you do some googling on the different breeds depending on what you like in a chicken as far as how the chook looks, egg colour, number of eggs, temperament etc
Bantams are a great choice for kids and make great pets.
Your pen and coop should handle 6 chooks fine, nice if you can let them free range a bit.
Post some photos of your coop and pen, as well as the chickens when you get them
