In some of these, the plot is an adventure and the parents are gone mostly so the kid can act heroically. Although there is some worry about the lost ones, clearly they need to be out of the way. Zita doesn't seem to trouble about her worried folks back on the home dimension, and Leanne, friend of the Cyborg, doesn't have a personality as much as a plot purpose, so her worries about her arrested mom come and go depending on what the plot would prefer. My kids never worry about the missing parents in these books either, which concerns me a bit. I ask them if they'd notice if I were gone, and they say probably, although if magic or robots start appearing they might be too busy. Fair enough.
In increasingly emotionally complex books, the parents are removed in a more realistic way. In Summer of the Gypsy Moths, two twelve year old girls desperately want to avoid foster care and so they conceal the death of their elderly guardian and survive alone in a house for a summer. May B.'s parents and employers manage to abandon her in a lonely sod house on the Kansas prairie with no way to get out or call for help. These last two are a good contrast, as May is capable of all the tasks she needs for survival, but is unwillingly alone and desperately lonely, while the lesser skilled Gypsy Moth girls not only have each other for support but could end their isolation at any time by admitting the truth. So while May cooks and manages and desperately tries to contact anyone, the Gypsy girls constantly fend off well-meaning adults to keep their isolation going while scrambling to feed themselves.
Cyborg: Clone Wars 2, Patricia, Frederick, & John McKissack. The writing is uneven enough to make me wish the author above had been pushier with her coauthors -- the characters' motivations and actions were often inexplicable (why didn't Houston tell anyone their ally was lying? Why did Leanne suddenly decide to give herself up without discussing it with her friends? Why did Toby suddenly show up a few pages before his help was essential?) It's like they think story doesn't matter if you are doing SF, especially SF with a message.
Legends of Zita the Spacegirl, Ben Hatke. My kids and I reallly like these graphic novels, with their attractive art and fast moving story lines. I found it interesting that Zita makes some big mistakes (stealing a spaceship) although my kids agree with her that it was just necessary. I also worry about her parents back home, which doesn't trouble the boys at all. We'll keep looking for more Zita.
The Summer of the Gypsy Moths, Sara Pennypacker. Classic story in the tradition of My Side of the Mountain, the Tillerman cycle, and other independent child tales, with two young girls fending for themselves after their foster parent dies. As an adult, I found the dead body creepier than my younger self would've, but the authentic voices of the girls and their often hilarious attempts to cover up their solitude more than made up for it. Very different from the Clementine books, but still good.
May B., Caroline Starr Rose. RML. Ooo, I strongly dislike poem novels. So I got mad when she did something silly even though she was only a kid. I liked that she went off on her own, even though only a coincidence saved her life.