Is there any relation between the two Mahou Tsukai ni Taisetsu na Koto series?
Someday's Dreamers: Summer Skies is basically the second season of Someday's dreamers made by another studio (Hal Film Maker) with a different staff. All it shares with the original is the fictional Tokyo backdrop, as as all characters and most of the setting have changed. 

You don't need to watch the first one in order to enjoy the second one.