Teaching young kids to write and read at a very early age causes interference in their natural learning style. reading and writing should be introduced from age 6 onwards. If your kid is below 6 years and having difficulty reading and writing, do not bother much as he will get better when his mind body coordination is fully developed to write and read.
Play and Primary schools curriculum which introduces writing and reading before age six interferes with children's natural learning. Kids learn on their own and from their environment, mostly by observation and exploration. They do not require structured learning before age 6 .