This is a difficult question to answer, because each child comes with his/her own strengths and weaknesses. Children learn to talk and express themselves at different ages, learn to walk at different ages and it is the same with reading.
I had always felt that reading stories to my children was of utmost importance. We do not use many of the words in ‘book language’ when we speak to our children. Through listening to stories, they learn at a fast rate the meanings of new words in the context of sentences, and sometimes use them in their speech, with occasional hilarious errors.
There are children, who at a very young age, will try and read names of goods in the supermarket, and have immediate recognition of them the next time they visit the shop. These children usually have a good visual memory, and will probably need very little help in getting going with reading.
My eldest daughter was like this before embarking on a reading programme. I was not a teacher at that time, but thought she should know her letter names and their sounds. By 3 years old she knew them all, and I then bought a reading scheme and she never looked back. By the age of 5 she was a fluent reader. BUT… she had great difficulties with spelling, and in later years, as she worked with her own children said, “Mum, if only you had explained the code to me, and how to sound out syllables in words, I would have understood how to spell accurately.” I mention this, because even if a child can learn to read visually, and subconsciously work the code out for himself/herself, it does not help with sequencing sounds for spelling.
My second daughter had poor visual memory at a young age. She could not learn to read visually until her visual attention span and visual memory had developed. This kicked in at 6 ½ years. I remember the headteacher telling me that I could not expect all my children to be University material, and I had to accept the fact that she was less able than her sister. WOW! That upset me! It was not the University bit, it was the fact she was judged to be less able. I knew she was sparky, had bright intelligent eyes, and was sure that she would get going when she was developmentally ready. When she was ready, I sent her to a friend who was a teacher, for extra lessons, and she never looked back and went to Cambridge!
My third child, a boy, was a different story. He was paralysed at the age of 4 ½, attacked by a little known virus, but luckily fought back, and learnt to walk and talk again. In his case there was neurological delay due to his illness, and he did not take off with reading until he was 9 ½ years old. I taught him his sounds, (but did not at that stage have a full understanding of the code), and struggled with reading daily. When he was ready, he took off with reading in a straight line, and went to University! He had a wonderful teacher when he was 9 years old, who built up his self-confidence and taught him to write poetry. He wrote many poems, with two words on each line, was praised and he never looked back.
My fourth child, a boy, had poor concentration and poor visual memory. His first school experience was disastrous. No allowances were made for this by his teacher. We were lucky to move to the U.S. at that stage, where at the age of 5 years old they are still in a Nursery Class. At the age of 6 he started reading, but only took off when he was 7 years old.
So when is a child ready to learn to read? All children are different, but all of them can learn their letter sounds and learn to break words up into sounds (segment) and push sounds together (blend).
They can chant the alphabet, as this is needed in later years for dictionary work, but to prevent confusion, don’t link the letters to the names until they know all their sounds.
If a child is keen aged 3, then go for it, if you want to. The child will let you know when he/she is ready to go. Read lots of wonderful stories to them, and look out for when they are keen to do some deciphering themselves.