It’s extremely rare for kids to spontaneously start reading. Most are either taught by their parents or by school. Interesting you mention that though because we get parents whose 6/7 year olds can’t read at all and they say ‘yeah but one day it will click’. Not necessarily.
Walking/talking - these are skills that are learned by watching care givers, experimenting, being encouraged. Walking tends to come more naturally albeit the physical environment needs to be supportive but talking absolutely needs input, Development of speech has a huge spectrum based partly on the amount of speech a child has been exposed to, how much they are spoken to (old landmark study showed that children didn’t learn language from TV nearly as well as from care givers - possibly because you can’t see the mouth shape as easily on TV), the way in which they’re spoken to (mirroring baby talk etc), whether they’ve got a dummy in constantly… and so on.
Likewise toilet training. My DD trained herself at 18 months - but she’d always gone with me to the toilet, I’d chatted about what I was doing, she was mirroring and then alongside that bladder and bowel control had developed quite early. My son needed to be taught it more overtly - which I did as soon as he turned 2. Waiting for them to do it themselves is part of the problem we have here.