Considering the premise 'And sometime during the third year, they can imagine objects and events with little or no support from the real world, as when they say to a play partner,  I'm calling Susie on the phone! ', is 'During the third year, none of them are able to imagine objects and events without support.' a statement that stands on its own?
And sometime during the third year, they can imagine objects and events with little or no support from the real world, as when they say to a play partner,  I'm calling Susie on the phone! ###During the third year, none of them are able to imagine objects and events without support.