Checkerface tells them that Only if their representative team wins the Representative Battle of the Rainbow, they can get their curse removed. However, the Vindice clarified that the Representative Battle is simply a battle to help Checkerface choose the new holders of the Arcobaleno Pacifiers. The current pacifier holders will die.
However, Tsuna, who does not want Reborn or any of the Arcobalenos to die, wanted to save them. So he went to seek assistance from Talbot, who managed to invent this machine that allows the pacifiers to keep working without having the need to feed off from their holders.
After the Vindice took over the pacifiers (By using their night flames to keep the sky flames running in the machine), the curse got removed from the current Arcobalenos and they will start aging slowly like normal infants. It's unsure whether they do age like normal infants or not but their will definitely start growing. The only one who went back to being an adult immediately was Lal Mirch because she did not have the full curse.