I'm fairly new to Savage Worlds but I've been running a game for my two 7-year-old boys and 10-year-old girl so I figured I'd share my experience. I think everyone's advice so far is good but I'll add lessons learned from my experience so far.
First off, it is working great! Everyone is having a blast and they're always begging to play more/longer. I decided to include one adult player to help focus the kids a bit when they get too far in the weeds but your idea of a second GM could serve that purpose as well (or even a single GM who doesn't mind stepping in to give them advice). In our case, I invited my mom to play with us. She had never played an RPG before but was thrilled to get the opportunity after having watched me play them as I grew up and spending time with the grand kids is always a bonus of course.
I keep the game very rules-light even for Savage Worlds. I'll briefly explain rules when they come up but for the most part I have them describe what they want to do and I tell them what kind of roll to make. They're slowly picking up the rules without me having to present a bunch of rules and boring them right off the bat.
At first I'd tell them what dice to roll in addition to saying "make a notice check" but they caught on pretty quick and now I just have to remind them on occasion to use their wild die. I can't stress enough how great Savage Worlds is at allowing a narrative style for the players to be easily translated in crunchy mechanics by the GM. It's let us have a ton of cinematic high-action adventures without having the kids get bogged down with worrying about the details.
I have been very slowly introducing combat tricks and tactics, usually in response to stuff the players want to do. I've kept the combats very lopsided so far to not force the issue too soon and that's been working great but as I've been slowly introducing harder encounters they've been stepping up their tactics naturally. The early combats were ridiculously skewed in the players' favor (4 pcs vs 2 weak mook goblins) but there was plenty of tension because the players had no idea how easy it should be and I played up the goblins being nasty little creatures. Use their lack of experience/jadded-ness to your advantage while you can.
With 2 GMs this is probably less of an issue for you but Savage Worlds really lends itself well to improvising as a GM. I have done almost no prep time for any of my sessions with the kids and have been using them as a exercise to get better at thinking on my feet. It's worked out great so far.
As others have said, kids love minis. The only caution I have about this is that when the minis are on the table my kids start treating it much more like a board game and role playing suffers. I've found that I have to clear the minis off the mat when we're not in combat or the boys get hung up on things like where their mini is relative to everyone else vs just describing what their doing.
The only other bit of advice I have is to keep the sessions short. I'm used to playing marathon sessions with my game group so short sessions have taken some getting used to. I try to make sure they have at least one combat per session but usually that's about it. Everyone is begging for more when we stop, but I know my 7-year-olds would start losing focus after about 2 hours if we didn't stop. Frankly, I've been really surprised that they manage to stay engaged for the 2 hours we usually play for.
Best of luck with your game!