The way we use adults can make or break a middle grade story. The primary audience for these books are kids who are beginning to spread their wings and establish independence. However, they are not yet as independent as young adults. They still rely heavily on adults for survival, even though they are beginning to develop their own ideas and friends are replacing parents as a primary influence. Adults, even those who mean well and want the best for the kids, are often seen as interfering.
When you look at many classic middle grade novels, the antagonists are often ineffectual adults. Look at James' aunts in James and the Giant Peach, Mathilda's parents and Miss Trunchbull, and the Dursleys. These characters tend to be either cruel or ridiculously stupid, or sometimes both. At the same time, the characters also benefit from supportive adults, such as Dumbledore or Miss Honey. This shows the relationship the middle grade characters have with the adult world that they are increasingly becoming a part of. Adults get in the way and cause many of the problems that need to be overcome, but they also offer support and comfort.
There has been a bit of a backlash lately against the "dead parents syndrome" in middle grade and young adult books. Many fear that by taking parents out of the story, kids don't learn that they can go to parents for help. But there's a reason why good, healthy parents are often bad for a story: the child antagonist needs to solve his or her own problems and overcome the antagonist with minimal adult interference. If the story includes supportive parents, then the temptation is there to have the parents protect the child and solve the problems. That's what good parents do. If the parents are in the story and don't solve the problems for their kids, there has to be a good reason why. Adults who take care of everything don't make for a very satisfying middle grade story.
The middle grade reader wants to see his or her peers overcome their own problems. The kids reading the story often don't have the tools yet to solve their own problems, especially when the problems are caused by adults, but they fantasize about the day when they can do it alone. They cheer when kids win, and cheer even louder when the kids beat adults. If adults step in and take care of things, then the adults win, not the kids.
It's perfectly fine, and probably a good thing, to give your child characters adult helpers. But those supportive adults need to be taken out of the story in one way or another at the end, forcing the child protagonist to fight the final battle alone. This is capital-I Important. The young character must win against seemingly insurmountable odds, and must win on his own without parents stepping in and fixing things. If the adult helpers are still present, this becomes more difficult, but not impossible. The child character must come up with the solution to the problem and solve it. If good parents are still in power, they are almost required by their position and because of their love to defeat the antagonist for their kids.
If you don't want to follow the common orphan path and want to include examples of great parents, that's fine, but make sure that the helpful adults are somehow removed so the child protagonist has to do his or her own protagging.