It is very easy to get caught up in so many activities that everyone is worn out. Children don't get the time and opportunity to play, pretend, and explore - all very important activities to learning.
Yet - I feel that there CAN be beneficial activities. Charlotte Mason advocated no lessons before age 6. I understand where she is coming from seeing how things are today. Yet - I have had personal benefits from music lessons as a youngster. I also was the child that learned to read by age 3 because my older sister decided to play "school" one day. (This was the early 70's - parents were GREATLY discouraged from teaching reading before school.) I needed to see the doctor often because of a heart murmer, and I was easily entertained with a deck of cards (learning a lot of math), or a few books, while I was waiting in the office. (Apparently I would entertain all the other people waiting as they would wait to see if I would see a card combination in a math game I would play...)
So - what to do? I say - keep it limited, keep it simple, and keep it fun!
I limit to generally 3 activities...
1) My children do swimming lessons at the Y from the time that they start to walk. For me, this is as much a safety issue as anything - it is good physical education, and my students love them! If my students didn't like them, we would still do them, but with breaks in between lessons instead of fairly continually.
2) My children do suzuki music lessons - see my post on music lessons
3) We do other occasional activities. For instance, we are currently taking a "Movement with Meaning" course - a "baby sign language" course for children age 2-5.
I do do some reading and math activities with my children, including some light phonics instruction. In our Kindergarten year of Year 0, we do a bit of reading most days. But only if the student is enjoying it.
What I DO do is make sure my Year 0 students have time to play, time to pretend, time to explore, and time outdoors. The little bit of scheduled activities we do are carefully limited. I occasionally get people suggesting that we should do this activity or that activity - and I have had to carefully consider what to include.
Note that these instructions are also important for Year K