My suggesstion is you need to get at the root of why they have reading problems. Do they have dyslexia? No interest in the subject matter? ADD? Difficulty with comprehension? The children need to be professionally evaluated, or at minimum asked why they are having trouble.
At one point I helped 4th graders who were below grade level in spelling and reading and I truly believe spending time with them helped them immensely. The teacher told me how pleased she was with their improvement. It was 4 children and I would help them with their workbook assignements. If they could not figure out an answer I gave it to them (that didn’t happen too often, mostly they worked things through with my help if they had a question). All the children improved their grades improve on tests.
I never liked reading, my comprehension was about average and my reading was very slow. I still read much slower than most adults from what I can tell. Reading for me as a kid was a lonely, boring, unfulfilling process. I still feel like that when I am not interested in the material, or if the reading is extensive.
My dad, he didn’t learn to read until 3rd grade. He hated school and teachers and was defiant. In 3rd grade he discovered comic books and kind of taught himself to read. Still, from the teacher’s point of view he wasn’t doing his work or reading much. But, the truth is from the comic book and then on reading was like a new world to him he loves books and reading and in his retirement went into the book business. He reads incredibly fast.