You are in a bit of a tricky situation with just youngsters, and the sole male being about half as old again as the females. Males develop faster than females anyway, and with their age gap, the issue is compounded. So first I'll offer some observations on your statements, and then some advice on going forward.
I tried to let my 16 week old cockerel and my 11 week old pullets free range today.
Good. Free ranging is good for all of them.
The cockerel was pecking some of the pullets in the face and their bodies
Has he been isolated until now? That is the impression I get. If so, everything is new to him and he is exploring the world with his beak, just as toddlers do with their mouths, as well as his eyes and ears etc. He wants to know what the other chickens are made of. The girls have grown up together so already know this stuff. Remember how much pecking of random items, including each other, they did as chicks.
he and I the leader of the pullets started really fighting (hackles up jumping and scratching at one another, etc). Is this normal behavior?
Yes it is. And that is just play fighting, testing one another out; they are all youngsters, they don't go in for the kill at this age. They can barely control their bodies properly yet. Think playground antics. The leader of the pullets is undertaking her responsibility to protect the rest from this intruder to their group, like a good big sister would with siblings.
Is it still too early to let them free range together?
Yes, because the male is so much older than the females. At 11 weeks they are really just like schoolgirls starting big school, whereas he's equivalent to a late teen boy leaving big school. If they were the same age and he'd grown up in their company, it would be a different story.
Right now the cockerel is in his own coop and run away from the pullets
Has he had any company thus far? Or has he had to grow up in solitary?
I also let the cockerel out and he will walk up against the pullets run and they will interact with the fencing of the run between them
That's good. Or the reverse (let the pullets out to go spend time hanging round his run).
he did go up behind him and peck him in the back of the head. It didn’t even hurt my 19 month old because he didn’t even notice, I just saw it
That's more exploring the world with his beak behaviour. He was probably intrigued by your child's hair. Or maybe there was a tasty insect walking on it.
Then after the girls were done free ranging and I put them back in their coop I let him out and he was fine.
I think that sounds promising, given where you are starting from.
Going forward, they need to get to know each other as well as possible before they interact freely, so any opportunities for him *or* the pullets to be out and able to go over to where the other(s) are confined would be beneficial. He needs company to grow up as a well-adjusted male; not just being able to see and hear female company from a distance, but close up.
You have to make a decision either: let them live together now and be prepared for a potentially brutal few weeks while he establishes his dominance and tries to mate with pullets who are not ready and will resist; or keep them separate but socialize them as much as possible through wire until the pullets have matured and are close to laying and seek out his attention. The latter will probably take at least 3 months and maybe more.
Don't hesitate to come back with more questions if you have them. Raising roos within a flock is only challenging at first. And it is well worth it imo. Good luck, whatever you decide to do.