While Kate is away, someone's taking full advantage to cause a ruckus a full blown incident. Is it Lewis and Anthony? It's the perfect timing to cause a distraction so Lou and Louise can be somehow rescued or "abducted" and sheltered to prevent unification. Could also be one of Edward's plots to make Kate look bad as a Star Bearer.
Either way, there's no coming back for Lou and Louise to the children's wing after getting invited. I don't think there's been any precedence of someone getting invited but somehow returning to the children's wing.