When your children play sports few people are as important in their lives or make as great of an impact as their coaches.
Of course, the best way to be involved in your children's interests is to volunteer to coach or assistant coach your children's teams.
Most importantly, you should remember to respect your children's coaches and treat them accordingly. You may not agree with all of their decisions, play calling, etc. But the fact still remains they are volunteers. They are volunteers who take time out of their own lives, time away from their jobs and families to help your children. They deserve to be treated with respect as such, especially if you aren't willing to do it yourself.
Some of the worst behavior I've seen directd towards coaches (even umpires & refs) has come from people who are in positions in the community who should absolutely know better and who should be setting good examples for our children not acting disgraceful in front of them.
DON'T BE THAT PERSON!!