It's up to you whether or not to sign them up year after year. If they love it, why not? The basic format is to build their robot, open the program, then begin to learn new skills.
Learning is built upon in subsequent years. There are several robot designs to choose from, and FVR uses a rotation of three different summer competition fields to learn with. A student who uses a field during 4th grade will find that same field a different experience three years later.
If you have more questions, FVR staff would be more than happy to discuss the options.