Fill it up, get the pump and filter going, and check for leaks.
If there was any FC in the water when it came out of the hose, it's all gone now. Consider it zero and add 3 FC. Give it a few minutes to spread out and it's safe to let kids in. They bathe in the same stuff, right?
You know there will be no CYA in there since tap water has none. You don't need to test for it, either. Mess around with the granules and the sock while the chlorine is mixing and put it in. Threaten the kids and tell them to leave it alone or they can't get in until it's all dissolved.
Then test pH and TA. If TA is below 50, raise it. If it's 50 or above, plug the numbers into poolmath and fix pH. You'll have to kick the kids out while you're messing with pH, for at least half an hour.
You should test CH just so you know what it is, not that there's anything to do about it. Low CH is no problem for a vinyl pool and there isn't a whole lot you can do about high CH since any replacement water will just be more of the same. There are steps to take to mitigate the risks of high CH, but don't worry about that yet.
And a word of advice on using poolmath. If your now reading is in range, that's your target. For example: say your pH is 7.3. Acceptable is 7.2 to 8.0. Ideal is 7.6 to 7.8. Don't target 7.7 and start micromanaging. Just leave it. If, however, your pH is outside of acceptable, then choose a target that is in the ideal range. Capiche?