You can file in CO, but unless you can show abuse of the kids, there is almost no chance that the court will let you take the older children back to GA with you. Courts try to maintain the status quo during the divorce process, unless there is a compelling reason to do otherwise.
The best thing that you could happen to you would be if you took the kids back to GA and the other parent did nothing for a few months, at which point a new status quo would be established. But, the risk is that as soon as you set foot in GA, the other parent files for divorce and the court orders the children's return.
That's why it's a toss up, because I can see different possible outcomes, but not enough knowledge of the various parties' dispositions to know what the more likely outcome may be.
Pretending for a moment, that I know nothing at all, I would say that filing in CO is a better plan, because it shows that you care more about the kids than yourself. But, that doesn't necessarily mean you will get the best outcome for yourself out of that decision.
How old are the two oldest, and are they male or female?