Wow, that's a lot of questions. I have a dd (8y.o.) & a ds ( almost 3). I didn't start hsing until after my dd finished kindergarten. However, even though I was a single working mom until she was almost done with Kindergarten, I had her ready for 1st grade when Kindergarten started. The most important thing I learned in my experience with helping my kids learn at very young ages, is to keep it fun. Fun is what will keep them interested, hold their attention, and have them asking for more. At that age, they're learning ALL DAY LONG. Everything is so new to them, they can't help but learn. As for a time limit for each activity, go until they want to stop.
According to many studies, the younger a child is, the easier it is for them to learn a foreign language. So, if you want to start them on one now, go for it. I've heard that Muzzy is pretty good for teaching languages to young kids. My dd is just now learning foreign languages, and I haven't started with my ds yet. So, I can't reccomend any programs, for that age, from personal experience.
For reading: First they need to be able to recognize the letters of the alphabet. My ds has learned this mainly from coloring pages I found online. With my dd, I played a lot of games to help her recognize them. We had a big vinyl mat that had the alphabet around it (all capitals). Sometimes, I would say a letter, she would find it & jump on it. Sometimes, I'd pull out flash cards with only lower case letters & she would play a matching game with them. We played other games too, I just can't remember them all. Something I've done for both kids, is to label things. I used index cards and made labels for things in their bedroom: WALL, DOOR, DRESSER, BED, etc. Some people say this is too much like a classroom, but it worked for us (my dd was reading before kindergarten). Point to words while reading to them. Read signs to them. Let them see you reading for fun. Keep lots of reading materials around the house for them. Things like that will encourage them to be avid readers.
For Math: Matching, patterns, counting, & shapes are all math. talk about the different shapes you see when you go out with them (or around the house). Count how many times you can bounce a ball. Make patterns with blocks or other objects around the house. I bought plastic animal counters for my ds (he loves animals). He'll spend 30min or more making patterns out them, grouping them by color or animal, and counting them. Have them match socks & then count how many pairs they made.
Basically, just keep it fun. Keep it light. Don't push too hard. They're going to learn no matter what you do. But, if you keep it fun & light, they'll enjoy it more. Arts & crafts projects, nature walks, helping in the garden or kitchen, listening to a variety of music, creative play, etc., will all teach them something. Don't forget that they are still young & need to enjoy their childhood. You can help them learn many things without taking that away, but if you push too hard or get impatient when they struggle with something they may start to get a negative attitude towards learning.
I hope these ideas help. At least, they may give you a place to start.