It depends on which version your child wants to watch.
Sailor Moon is a great series, though I prefer the subbed version. The English dubbed was made for younger kids while the subtitled one was rated PG-13 due to language, same gender romance (mainly Sailor Neptune and Sailor Uranus), and cross-dressing. Here is mainly what the story is about, Usagi Tsukino (Serena Tsukino in the dub) was a lazy, clumsy, 14 year old cry-baby until she rescued a purple cat with a yellow cresent mark on her fore-head, named Luna. Luna, spied on Usagi for a while and finally, sure she was the one, confronted Usagi, showing her how to transform into one of the Sailor Senshi (Sailor Scouts in the dub), Sailor Moon, and eventually finding the others of Sailor Senshi. Characters: Sailor Moon/Usagi Tsukino/Serena Tsukino, Sailor Mercury/Ami Mizuno/Amy Mizuno, Sailor Mars/Rei Hino/Raye Hino, Sailor Jupiter/Makato Kino/Lita Kino, Sailor Venus/Minako Aino/Mina Aino, Sailor Chibi Moon/Sailor Mini Moon/Chibiusa/Rini (her last name is not given, but she is Tuxedo Mask's and Sailor Moon's daughter who travels through time to help the Sailor Senshi), Tuxedo Mask/Mamoru Chiba/Darien Sheilds (Usagi's boyfriend/husband) Luna (dark purple cat), Artemis (Minako/Mina's white cat. Fun fact: all though Artemis is the name of a a greek godess, Artemis is a male cat), Diana (light purple kitten of Artemis and Luna from the future), Luna P. (Chibiusa/Rini's robot ball thing which is an impression of Luna), Sailor Uranus/Haruka Tenoh/Amara Tenoh, Sailor Neptune/Michiru Kaioh/Michelle Kaioh (Fun fact: In the subbed and manga, Sailor Neptune and Sailor Uranus are in love, but, in the dub, they are VERY close cousins), Sailor Saturn/Hotaru Tomoe, Sailor Pluto/Setsuna Meioh/Trista Meioh. Hope this helped you decide! ^_^