First, at that young of an age, you have a lot of control and I would say expose them to as many play opportunities as possible. Let them guide how much they want to do. If they want to kick the soccer ball around, go kick it around. Don't worry about teaching them how to do it, just let them do it and have fun.
Second, I would say enroll them in a gymnastics class to learn some basic movement skills. Ideally they learn a little about jumping, landing, and tumbling. Learning how to fall is a really, really good skill.
Focus on effort and process and not outcomes. There is a range between cheering for them lacing up their cleats (now if that is how they learn to tie their shoes then some celebration of them doing it the first time is warranted) and never giving them encouragement.
Have them play a lot of sports and give them the equipment just to go out on their own and PLAY!!!!! Have all sorts of balls around (sized appropriately) and let them just pick one up and PLAY. If they are shooting the soccer ball into the goal, let them.
They are 6 and 8, if you are getting on them for making a bad play then you really should not be a parent. Also, unless you are the coach, do not coach from the bleachers. Yelling instructions at your child is one of the many stupid things parents do.
Praise effort. A kid (or adult) can do everything "right" and the outcome can still be negative. I can hit a beautiful forehand and if my tennis opponent cheats that way and volleys it into the net, I still hit a great forehand.
Set up a climate that recognizes "failure" and mistakes as part of the learning process. If a kid fears failing (and your reaction) they will not try new and challenging things.
I would say read up on the idea of the growth mindset, read Rob Gray's book on how we learn to move, check out Project Play. Also, here is some stuff from the USOPC.
https://www.teamusa.org/About-the-USOPC/Coaching-Education/American-Development-Model/For-ParentsI would also say check out
www.admkids.com. It is a hockey site, but a lot of info is good for parents of other sports.