Below are many websites about Jewish holidays ranging from laws and customs to games and recipes.  For your convenience, the sites are hyperlinked.

Rosh Hashanah
http://www.jr.co.il/hotsites/j-hdayrh.htm

Yom Kippur
http://www.jr.co.il/hotsites/j-hdayyk.htm

Chanukkah
http://www.jr.co.il/hotsites/j-hdaych.htm

Sukkot
http://www.jr.co.il/hotsites/j-hdaysu.htm

Tu B'Shvat
http://www.jr.co.il/hotsites/j-hdaytu.htm

Purim
http://www.jr.co.il/hotsites/j-hdaypu.htm

Passover
http://www.jr.co.il/hotsites/j-hdaypa.htm

Yom Ha'atzmaut
http://www.jr.co.il/hotsites/j-hdayil.htm

Yom HaShoah
http://www.jr.co.il/hotsites/j-holoc.htm

Lag B'Omer
http://www.jr.co.il/hotsites/j-hdayla.htm

Shavuot
http://www.jr.co.il/hotsites/j-hdaysh.htm

Tisha B'Av
http://www.jr.co.il/hotsites/j-hdayav.htm

Tu B'Av
http://www.jr.co.il/hotsites/j-htubav.htm

Yom Yerushalayim
http://www.jr.co.il/hotsites/j-jer.htm

For more holidays go to:
http://www.jr.co.il/hotsites/j-hday.htm

Your Source for Summer Activities
http://www.jajz-ed.org.il/summer/index.htm