I don't know if the breed matters, but age certainly does.
I have a dozen 5 week old mixed ducklings without a mama, and 6 two week old ducklings With a mum (Cindy.)
I let them all go into the same pen with a wading pool, a smaller pan for the little ducklings, 2 full food dishes and extra bowls of drinking water.
Cindy immediately chased all the older ducklings away from her babies and commandeered the wading pool. One of the older ducklings kept going back to the pool instead of joining its siblings in the duck hut, so Cindy grabbed him by the head fuzz, jumped on his back and started stomping the daylights out of him. I separated them so she wouldn't kill him, and let her take her babies out to the yard at large, leaving the older ducklings confined in the pen.
The 3 'teen' ducklings (April hatch about 10 weeks old) and other two adult female ducks do not bother the little family, and Cindy does not chase them. They all sort of skirt each other in passing. I have my 2 drakes penned up with my chicken flock. George the rooster keeps the drakes in line so there's no funny business going on there.
I would not introduce your older ducklings to the families unless you have plenty of space for all groups to feel separate and safe from each other. I would also supervise closely and intervene if there is any ducky mayhem going on. Mother ducks can get mean and they do mean business.