Congrats on wanting to get in there and teach and play with your kids. I know a lot of your day involves the newest baby, too which is a challenge. I'd recommend that you plan out your day as much as possible. Find a great routine that includes: daily chores that the kids can either help with or do on there own, time for reading with each one individually and together, a "theme" activity that's relevant to them, some sort of hands-on play, and anything else you'd think they'd enjoy. There are lots of preschool websites that will help give you ideas. I definitely encourage you to pick a theme that you focus on for a week or two at a time and develop activities around the theme. For example, right now is a great time to talk about fall harvest. You can get books about apples, pumpkins, and fall in general from the library. You can then move into "Manners" or "Thankfullness" as Thanksgiving approaches and so on. Here are some simple theme ideas: November: Thanksgiving December: The meaning of Christmas, Holiday Traditions, January: Winter/Snow February: Healthy Teeth and Healthy Hearts, March: weather, spring, April: animals, flowers, May: summer, bugs, June: ice cream, construction, July: flags, vacations, August: grass and snakes, September: apples, nocturnal animals, October: spiders, fairy tales.
The 4 and 3 year old can begin to learn letters and their sounds, numbers, counting objects, sorting objects based on their characteristics. The 14 month old can be learning colors and shapes and language in general. Sign language is great if you haven't done that yet. Remember that little attention spans are short, so 15 mintues is really tops for an activity/story. Also, don't expect them to be able to sit for long periods of time and work on something or listen. It's just not in their nature. I'd try to balance free play, sit, get up and move around, read, etc. so that their constantly switching it up. It takes longer at first, but teaching them independence really is one of the greatest gifts you can give yourself and your children. Allow them to pick out their clothes, dress themselves, take care of their laundry, make their beds, brush their teeth, put away their toys and books, help mommy with laundry, help mommy cook, help mommy with the baby. Be right there with them and model the correct way and allow them to try it out. Allow them to fail (as long as no one is going to be hurt) and reteach as necessary. This does take MUCH longer, but it really does pay off. In every activity, try to figure out how they can be involved or how they can do it themselves. Can they dress/undress for pottying? Can they flush? Can they wash their own hands? Can they turn the light off and on?
Here's a sample schedule to give you an idea of what I mean:
7:30 wake up (kids pick out clothes, dress, make bed, brush teeth, bring dirty clothes to washer)
8:00 Breakfast (14 month old gives everyone a napkin, 3 year old gives every one a spoon, 4 year old helps pour cereal, etc)
8:30 laundry - 3 and 4 year old help swap loads and sort the clothes into piles such as these are mommies, these are big sisters, these are mine, these are brothers, etc.
9:00 Story time/free play - while 2 are playing sit down with one and read a story together. The 14 month old might not be ready for all the words on the page, so point out what you see in the pictures and practice naming things: cat, moon, oh look, she looks sad and so on. Rotate them through this until everyone has had a turn.
10:00 Playdough or craft. Use online preschool sources (I like: perpetual preschool, homeschooling.about.com, first-school, and AmblesideOnline.org) to find something to do. If they want to color, great! If you want to bust out the shaving cream and have them play in it - it's awesome. It cleans up your table nicely and the whole room and your children smell fresh and clean afterwards! :)
10:30Free Play
11:00Story or fingerplay or song that fits the theme.
11:30 Math or science time - practice counting leaves (you can make them out of paper if you can't fetch them from outside), discover what happens when you put lemon juice on a sliced apple and leave one apple without the lemon juice. Compare the results. Explore the parts of an apple, and so on. Play with puzzles (yes, that's math), play simon says, play "I spy" play "I'm thinking of a word that starts with.... and is blue" etc.
There are a million opportunities to talk about science and math in everyday household chores. You can learn about ice, water, and steam easily in your kitchen. You can talk about why mommy can touch the pan in the oven with the mitts on, but can't with them off. You can talk about bubbles in soap, what's in dust, why we need to brush our teeth, how to follow a recipe, how to properly care for different types of food (this can stay in the pantry, but this has to go in the fridge or it gets bad), why we keep things clean, why we keep the windows and doors closed in the summer, but open in the fall, what happens to the sun at night, why the sun sets, our bodies and their parts, how to stay healthy and so on. Just start to think of every little thing that you're doing and talk while you do it, even to the baby when you're changing a diaper. Your 4 year old can bag up the garbage and take it outside. Your 3 year old can clean with a dust rag or feather duster, your 14 month old can take "this" and put it "over there"