Of course, Code Studio level 1 is the easiest way to introduce kindergarten and first-grade students to code. I love it, but during Computer Science Education Week, it often has performance issues because of the huge amount of traffic that is generated. While it is wonderful, I always have a fallback plan in case it goes down or is just too slow. I set up my student accounts the following week because Code.org does not track progress that week anyway, due to the volume of users. I would like to recommend a couple of the third party sites as an alternative.
Code Monkey is both more game-like and more like real computer code than most of the other options. While I love Blockly, which is used by Code.org, Code Monkey has students making a product that actually looks like a computer program, down to the numbered lines. Students do need to be able to read to be successful, so I would recommend Code Monkey for students ages 7 and up. This is my go-to site for grades 2 and 3, after Code.org.
The Foos are extremely game like and need no reading or written language. All students love it, but it is especially great for English Language Learners. The logic makes it difficult for kindergarten because it is not as simple as it appears to solve the levels. I would use this in any situation where reading might be an obstacle to student success.
Scratch has a great project called Make It Fly for #Csedweek. Of course, Scratch requires reading and is a bit complicated for beginners, but this is a really enjoyable animation project for upper elementary and beyond. If you have IPads or Android tablets, ScratchJr is perfect for the youngest learners. No reading is required and it is so intuitive that my kindergarteners were teaching their teachers.
Tynker has a great beginner activity called Candy Quest. I have used this successfully with kindergarten and first grade. No reading is required. I hope you choose some engaging activities for your students or your own children for Hour of Code and throughout the year.