I have younger siblings (as young as 6)and want to watch an appropriate Anime

Yugioh
Pokemon
Yugioh GX
Mew Mew Power
Sonic X
Yugioh 5D
Sailor Moon

Dragon Drive (:

First I suggest Ghibli movies:
Tonari no Totoro
Laputa: schloss in the Sky
Secret World of Arriety
Ponyo
Kiki's delivery service
Pom Poko
Spirited Away (it might be scary for some children that age but still...)
The Cat Returns
My Neighbors the Yamadas
Porco Rosso
Whisper of the herz

Totoro will most likely will be their new Favorit Mikey maus

Others:
Unico
wolf Children
Tokyo Godfathers
Children who chase Lost voices

Digimon
Pokemon
Sailor Moon
DBZ
Princess Tutu
Astro Boy

Cardcaptor Sakura

Fancy Lala is both adorable and appropriate.

Here's the first episode.

It might depend on their gender, but how about Shugo Chara? It's cute, has a lot of episodes, and is inspiring.

HighschoolDxD HaHaHaHaHA!!!!!!

Try Pretty Cure!

save me Lolipop! might be a good one XD

Princess Tutu was a really good Anime for younger kids, especially if they enjoy dance oder ballet!