If the kids are not reticketed in J, C, D, I, or R class, then they will not be able to travel in First as check in will fail. Are all four of you on the same PNR?

If you are traveling on an otherwise busy route or date where the plane may be full, you may want to be careful as there may no longer be 4 seats together in coach

​​​​​​​What what route and plane are you scheduled on currently? Was there an equipment swap of some sort?

​​​I'm not trying to s+&# on your parade, just don't want your hopes to get too high. There is also the very real risk of the rebooking screwing up the e-ticket which may cause severe headaches on the actual travel date, so it really would likely work to your benefit to make sure it's all sorted before you leave for the airport if this is an important trip.