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If you bring younger kids, aged twelve & under, to Universal Studios, they will probably be most interested in the Nickelodeon Blast Zone. Featuring three attractions in 1, this is one of the few attractions that really appeal to the younger crowd at Universal Studios Tours, so you can expect them to spend a great deal of time there.
Shaped like a huge orange rocket, the Nickelodeon Blast Zone is a big hit. This is a huge play location basically - and it is unlike any playground that your kids have ever experienced. There are three sections of the playground: The Wild Thornberry's Adventure Temple, Nickelodeon Splash, and The Nick Jr. Backyard.
The Nick Jr. Backyard is the only area in Universal Studios that will be of any interest to toddlers. In fact, it is the only safe place for toddlers. If you bring a toddler with you to Universal Studios Tours, plan to spend the entire day here. Nickelodeon Splash is a water area. Bring a change of dry clothes, because the kids will get soaked here. They can fill buckets of water in a fun variety of ways, create waterfalls, and stand under waterfalls. There are also many mounted water guns to be used and enjoyed.
The Wild Thornberrys Adventure Temple is an extensive playground. While here, you will have foam balls flying through the air all over the place - the kids are able to shoot and throw them, and since they are made of soft foam, they are safe. The kids can also meet many characters here, including the Rugrats and Blue's Clues Characters. The attraction is located on the upper lot, and is open everyday that the park is open. If you don't want your child to get wet, avoid this attraction altogether, because with all of the water flying almost and being dumped, there is really no way to avoid getting wet. If your child is too young to enjoy the attraction by themselves, you will be getting wet as well.
Overall, this is the only attraction that younger kids will enjoy at Universal Studios Tours. As a parent or guardian, you should expect to spend most of your time here, and you should never leave your child unattended. This is not a place to drop your kids off for the day while you go enjoy other attractions. Instead, use the buddy system with other responsible adults in your party - one should stay with the kids, while the other adults go enjoy the attractions, and relieve each other often so every person has fun.