There is alot of good advice out there, including this link.
http://www.felinebehaviorsolutions.com/ ... -patience/Besides the safe room concept and taking it slow, they mention using a sock to exchange scents. Helping them be comfortable with each others scent is key. I have in the past used baby powder or a spritz of cologne to make them all smell the same, but no longer recommend using anything that might be toxic. But there are yummy things you could smear on all 3 like wet cat food or tuna. Confuse their senses. Besides if the cute kitten has cat food smeared all over it, the older kitties just might have to lick it off.
This might also be a good time to use FELIWAY pheromone diffusers and/or Sargeant's Calming Collars to put smells of friendship in the air.
Give more attention to the older cats, and avoid showering the cute ittie bittie sweet adorable piece of fluff with too much attention in front of the other cats. Maybe only your daughter should handle the kitten at first. You want to avoid jealousy.
And this may sound crazy, but talk to the older cats and tell them you got THEM a new pet and playmate. That the kitten is THEIR kitten.
Here is another trick. Have your daughter hold the kitten and cause it to meow pitifully. That might bring the older cats running to protect it. Once they identify it as something they should protect, they should have fewer issues.