Ducks bullied by chicks

We have 4 call ducklings which are now nearly fully grown and have lived in the run for 4 weeks, 2 weeks ago we got 4 chicks which have lived inside the coop for the 2 weeks as not old enough to roam yet. Yesterday we let the chicks out with the ducks and the ducks was fritened of them. The chicks chased the ducks off the grass and the 2 kept there distance. We was hoping they would all live together happily.
Should we continue to let them roam together or should we move the chicks into another section (which we have ajoining run)

We was hoping to get a couple of geese and thought they might help protect all!