We adopted two skittish cats from the same home and started them in a bathroom with a tile floor (which was where the litter box ended up living). This was the advice of the rescue group. I do think it helped. After a couple days, we let them out during the day on one floor (kids at school) and put them in the bathroom at night, and gradually expanded. I thought it seems cruel to lock them in a small space until I let them out. They headed as far under the beds into corners as they could go and refused to come out for any reason.
One word of caution. The cats may be used to a 4 year old, but is your 4 year old used to cats? You have to really keep an eye on that because 4 year olds love to chase, pet the wrong way and dress cats up like baby dolls. And if the cats have claws, they might fight back.