I have a LP Fuzion, Mausingfield and a LA Defiance Deviant all with BnA Tacsport triggers. The bolt lift on all of them is very light - I wouldn't think that any kids would have issues with any of these actions with properly timed triggers.
When it comes to bolt lift, you need to understand that a properly timed trigger will optimize your bolt lift, keeping it as light as possible. This can be done by a gunsmith, the action manufacturer (Bighorn/Zermatt provides this service, I believe for free), or with a trigger such as a BnA Tacsport, you can easily do it yourself at home. My friends Mausingfield with an untimed trigger is unbearably heavy when compared to mine, and for the brief time I owned a TL3, the sear engagement was so heavy that the bolt lift and close was impossibly heavy.
For light bolt lifts, you are always going to have a lighter lift with a 90* action then a 60* action. Also, different actions cock differently. Both the Mausingfield and LP cock 100% on open, meaning all the work is done while opening the bolt, and they essentially want to close themselves. Other actions, like Impact, spreads the work of cocking the firing piece over the open and close (50/50). I'm not sure what your kids may prefer, but I prefer 100/0 (cock on open), the rifles already unsettled through recoil, I'm not worried about further disturbing the sight picture when opening the bolt, but I like to have my sights on target by the time I start closing the bolt.
Beyond that, an action is very much a personal preference. My wife has the LP Fuzion, and she loves it. It's a great action, one I would certainly recommend. I love my M5 Mausingfield, but have no experience with the newer ones.
If you don't want to change out bolts/bolt faces for different cartridges in the future, you may want to consider a straight up 6BR. It will have a bit more recoil then a .223 - I'm not sure how big your kids are, and how recoil sensitive they may be, and you will also need to reload for this cartridge. Nothing wrong with the .223, that's also a great round and you can "grow" into a 6ARC on the same bolt face. Just spit balling ideas.
I think the KRG Bravo is a great chassis that's very affordable, has plenty of accessories to dress it up and allow it to "grow" with you/kids as you progress, and it's light. However, minimum length of pull is 12.8" according to KRG's website. I don't have kids, so I don't have a good handle on chassis options that are best for kids/shooters with short LOP. It's hard to find on their website, but McMillan has a stock designed for junior/smaller shooters, called the A-10 that's also worth a look:
Not all rifle shooters are created equal... Some have smaller stature. Ladies, on average, have smaller torsos and shorter arms than men. Junior shooters are also smaller than adults.
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