There are so many 'Mommy' feeling swimming around my head after I read your post...but, as someone who has been in the education field for more than 10 years, I will tell you that kids are not 'ready' for structured daily work plan until at least 7 years old. That's why first grade introduces workbooks, flashcard systems and reader programs. I have worked with kids k-2 in informal education and formal education, and from my perspective toddlers need a less structured atmosphere that is more about discovery and less about sitting down and completing tasks.
I would recommend going to several pre-schools in your area and asking to view their curriculim. From there you can get ideas of how to structure your son's day, and your 21 month old may benefit from this too. In kindergarten, we created a routine that is centered around understanding your environment, and working creatively, as well as introducing the concept of teamwork and helping. The main focus at least for me as a teacher has always been the core basics, shapes, colors, number and letters. From there kids work at their own pace, and this helps me as a teacher to see what kinds of learners I have in my room. From there, I work with kids on the core lessons of what the state guidelines require and I group kids in groups of various learning types so they can 'help' each other throughout our time together. But, even in kindergarten I avoid worksheets and tasks that may be frustrated or confusing to the kids...quick and concise is the key to creating a fun and energetic environment that allows kids to feel accomplished and excited. I also, fought to have a garden in my play area, so at the beginning of the year we plant stuff and watch it's progress...kids love feeling like they are a part of 'making' something. I even have a garden in our backyard that my son, Grandpa and I tend to almost daily.
Things like a gold fish can teach responsibility, while having fun and learning about fish life. Then we take a visit to the Long Beach Aquarum. Umm, let's see...there is so much I have to share...learning can be fun and exciting for kids, you've just got to build it around things that don't appear to be learning. We have a rewards program, but it's for completing regular tasks like putting things away, feeding the gold fish, helping with snack...at the end of the week, those who have a full row points towards prizes. The prizes are always stuff like books, $5 GC to Borders, extra time on the computer, free play or something that is encouraging learning.
It is really important to work with kids at their own pace, and not try to create a learner but, encourage them via their learning abilities. I am a visual and audio learner, but I hate sitting and doing worksheets and completing unguided activities. I hate the labels of ADD and ADHD, my son's Dad was labeled that way and on more meds during his childhood than necessary to 'control' his behavior and he missed out on so much...even today he labels himself as the 'not smart' one. It's terrible.
My son is now 2, and I work during the day...he's with Dad in the morning and their focus is structured play outside and they go visit the park, botanical gardens, zoo and other local places where 'hands-on' learning can happen. Then he goes home and has lunch and nap with Grandma, and when they wake up she does activites with him like blocks, shapes, letter and numbers...Lakeshore has great toddler age stuff for pre-learners. He loves to read books and color, but his day doesn't revolve around 'learning' and what he needs to 'learn' but, exposing him to things that will encourage learning and development.
You have your hands full, but you can do it. I would sit down with your hubby and create a game plan for how to work with your son, and avoid comments that will discourage him from wanting to be a part of a learning environment. My son has a space where he can do his thing, we got him a little desk that he picked out at Ikea, an easel where we do painting, a table and chairs that are his size and we try out best to do everything on his level. If you create a 'learning' space that is special for him, this might help him create a sense of ownership over the 'learning'.
I really wish you and yours the best of luck!!