Some kids are just like it I'm afraid. My daughter goes in with tight braids and comes back out as stig of the dump
Pretty much what I was coming on to say!
My dd has thick, curly hair which is murder to be honest.
But still I endeavoured to have her neat and tidy for school. Never lasted more than a few mins as dd just wasn't that kinda kid!
We (the WHOLE family) have an "infamous" school photo of her, taken first thing that day, I'd sent her in perfectly neat and tidy with the wild curls tamed into 2 plaits, new cardigan (Cos shed already wrecked the other 2) etc...
In the photo
No cardigan
Tie at half mast
Smudge of mud on her cheek (god knows how she'd not been outside)
And only 1 plait still in place the other completely undone and the hair a total frizz explosion! 
I was so stressed and embarrassed at the time...now I love it!
It PERFECTLY embodies the child she was at that time, fun and carefree (tearing about getting into scrapes), generous (she'd given the elastic from her plait to a friend who was in tears as they'd lost theirs) and confident (HUGE cheesy grin in the pic)
And that's why it's the one pic the WHOLE family has!
Embrace it op, let them be a child it's such a short time when they're like this. Given their age would a little fringeless bob be the best option ? The trouble with fringes is they quickly grow and get in the eyes and require a lot of maintenance, or as pps say a long style but worn in a plait maybe a french plait?
My dd is now almost 20 and not only rarely seen with a hair out of place but also rarely seen make up free. She's beautiful but I wish she were more confident in herself and more like that carefree 7 year old now.