When I’m helping prospective coaches pick which side of this split to fall on, there’s a few questions to ask. I’m going to use the word “you” several times here - I’m really referring to both you, the adult coach, and the student participants.
What are you trying to get from doing this?
If you’re just looking for an activity to do, and only want it to run for a predetermined number of weeks, Explore is great. Do the lessons included, wrap up, and be done.
If you’re looking for something that more closely resembles FTC or FRC, in that you can theoretically infinitely refine your robot and innovation project, Challenge is the way to go. There are core lessons to be taught, but you can always learn more advanced programming and do more serious research.
What do you find fun?
If you’re a nerd (like me), the idea of programming your very own robot to do missions is super fun. As a kid, I’ve bought in to the idea that I want to do this thing, and I don’t need to be pursuaded to participate. Challenge can be daunting, and Explore can serve as a great intro in one year, before they move into Challenge.
Do you plan on doing this again next year?
If you’re planning on doing this for several years, and you want to research and planning you do to carry over, Challenge will allow you to do that. Explore is to Challenge as Challenge is to FTC.
Will losing destroy you?
As a 4th grader, you’re probably going to lose to an 8th grader - I’m just being honest here. I’ve seen the opposite happen, but it’s rare. If you can’t stomach the idea of losing, starting with Explore can give you time to mature, but still work as a team to do a thing.
Personally, if there isn’t a reason you can’t do Challenge, I’d go for it. It’s a ton of fun, your experience as an FRC coach will have some relevance, and the skills the kids learn will carry over better in to subsequent years (both in Challenge and FTC/FRC).