I am always looking for new websites to challenge my students. From introducing a concept to reviewing/reinforcing something we have done in class, my students enjoy the online activities I share with them - such as BrainPop's Food Fight! My kids were so engaged with the game they wanted to do a tournament to see how could survive the longest. We used the randomizer available at https://www.superteachertools.us/instantclassroom/random-name-generator.php#.VkogtL8YOSo to pick our animals for each round.
My go to source for new sites is http://interactivesites.weebly.com/. They offer an assortment of websites for all subjects and topics. I'm sure you'll find something new to use with your kids!