We just try to get around our chickens a ducks regularly. We are not aiming for every bird to be willing to sit in our lap, but friendly is important and aggression towards people is not tolerated. With 2 little kids (the human kind) it's important that the chickens and duck don't peck, bite, scratch, etc. We allow them to have their disputes amongst themselves, but with people it's friendly or feel free to stay out of people's way - act out of line and you become dinner.
That said, we raise chicks from hatch or just a few days old indoors with the kids involved in feeding and caring for (and petting) the birds. Several chickens allow the kids to run up and pick them up. The ducks just tolerate human presence generally, but will come running into the coop for feed if we step into there which is amusing for the kids (and very loud for us adults).