I have observed that letting little children learn on their own is a great precedent for curious, independent learners later. I have both a 4 & 5yo. My 5yo is in Kindergarten. Her only requirements are Bible reading, memory work, and then I have about a half hour or less with her where we do a few minutes of copywork, some math (I just use books or manipulatives and work on different things like reading a clock or simple addition), and then she reads to me from her readers.
Because I have an older child my two youngest join him for a lot because they like beig all together with me. So yes, my 4yo is listening to Robin Hood and learning Spanish but my oldest never did things like that!
Charlotte Mason recommended children begin formal schooling at age 6.
Until then I focus on reading lots of good early years books and add the 3Rs as we go. As far as being ready my youngest knows all her letters and their sounds – but 3 months ago when she asked to learn to read I would show her the letter and she knew the name but after teaching her the sound she would forget it everyday! So I told her we would wait a little while and I gave her the letter flash cards. She would sometimes ask me the sounds and lo and behold she now knows them all without mommy having to drill every day and get frustrated. So I tried to move her on to blend letters to make little words – brick wall! So I backed off and we just kept practicing sounds. The past week she has started picking out little words herself – ok she is ready to move on!
If they pick it up within a few days they are developmentally ready (for most children with no learning issues) but if you have to retract something over and over you are just frustrating both of you. The same with writing. My daughters picked up writing so easy but my son didn’t write easily until this year (2nd grade) so I went slowly with him. My 5yo already does a whole line of cursive copywork at a time. Every child has different speeds in different subjects.
Just relax. 🙂 outside play and good books at nap time are the best preschool!