The claim made by the Twitter post originated from information that was given in a New York Times article by Hannah Dreier.
It's an account of different children of migrant families such as Carolina Yoc, a 15 year old who was working in the Cheeto factory in Grand Rapids, Michigan.
The article explains how many of these children are being used as workers, saying, "The factory was full of underage workers like Carolina, who had crossed the Southern border by themselves and were now spending late hours bent over hazardous machinery, in violation of child labor laws. At nearby plants, other children were tending giant ovens to make Chewy and Nature Valley granola bars and packing bags of Lucky Charms and Cheetos — all of them working for the processing giant Hearthside Food Solutions, which would ship these products around the country."
Also, the article accounted for this illegal child labor across the country, it said, "Migrant child labor benefits both under-the-table operations and global corporations, The Times found. In Los Angeles, children stitch “Made in America” tags into J. Crew shirts. They bake dinner rolls sold at Walmart and Target, process milk used in Ben & Jerry’s ice cream and help debone chicken sold at Whole Foods. As recently as the fall, middle-schoolers made Fruit of the Loom socks in Alabama. In Michigan, children make auto parts used by Ford and General Motors."
There is a lot more information within the article about how these companies were able to sneak around laws by not documenting the children as workers, leading to many undisclosed deaths and horrible treatment.
I was not able to find any direct information that half of the workforce has disappeared. However, the author of the article did tweet out, "Hearthside Food Solutions—which makes and packages Cheetos, Cheerios and Chewy Bars—has begun going through its 39 factories to check for children. Workers say much of the staff has vanished overnight.". It seems as though based off the information given by Dreier's other sources working in the factories a large portion of the workforce was children.
Even without clear evidence of the exact amount of children working in the Cheeto factories, based on the fact that the main article where the claim was derived from had such clear and thorough evidence, I believe that part of the claim about the children in the work for is true, but that half the workforce was lost is exaggerated.
https://www.nytimes.com/2023/02/25/us/unaccompanied-migrant-child-workers-exploitation.html
https://twitter.com/hannahdreier/status/1630651131486502912/photo/1