How tall is your fence? I have 6 ft privacy fence and none of my chickens have flown over it, yet. You can clip wings if it becomes a problem but I would not worry about it until you get an escapee.
I have 1 leghorn in the bunch and she is able to fly over their 6ft tall fence, she did it and wandered around but when I went to check on her, she was back in the fence with the others that are too fat to get that high. Now she stays with the rest but everynow and then she likes to explore---she's the free spirit of the group
I understand your concern. I too want to let my chicks free range some but I am worried they won't be able to find their way back in the coop/run gate. I mean they don't know anything about the yard outside of their run, what if they get lost or decide they are going to roost on a tree branch instead of going back to the coop? If I decide to let them out to free range, do I just open the coop/run gate and let them decide if they want to go out or do I herd them out of the run? Oh and what about my 15 guinea keets? They are currently kept with the chicks in the coop/run so do I let them out to free range with the chicks or are they likely not to come back to the coop/run and therefore lead the chicks away too? Gosh so many questions and concerns!!!
If they have been regularly going to roost at night in your coop they will just march on in the coop at dusk when they are free ranging. Mine started by sticking close to the coop and then gradually spanning out. After a few weeks, they had claimed the entire yard. I do have my yard fenced but I know of others who have large fields or pastures and their chickens come back home to roost.
4 foot high fence and they have never went over it. They stay put in my yard and there fine. Give them love, goodies and a yard and there going to stay put. My girls go into the coop at night through the run door and put them selves to bed lol. There 5 months old. I suggest you hold your babies, and love on them, they will be tame then when you put them in the yard. We did and our girls are very friendly.