As parents, we are happy whenever our kids learn new things even not yet going to school. There are ways in teaching them especially toddlers, age 1 to 4. These age range of kids are probably the best age to start teaching them because their minds are still so fresh and innocent. Having a kid of my own, I had to find ways to teach my kid in a way that he is not pressured.
If your kids are at the age of learning new words or in the process of improving their skills in reading and talking, try to communicate with them as often as possible. They say be talkative with them. Talk about everything you see and touch, in that way your kids will absorbs them in just a snap. If you are busy and a little bit bothered by your kids naughtiness, let him/her watch barney or other video materials with singing and dancing that help them improve their vocabulary. After watching, ask them what did they watch. Based on my experience, whenever my son finished watching, he is always coming to me and tell me what he saw and making some actions and then he tries to connect it with some of his previous videos he watch or to the his life. For example, he got interested in the airplane, he will tell stories that he will gonna fly with the airplane together with mama and papa and we visit oma and opa (lola and lolo in deutsch, they are based in germany).
Try to play with them also as often as you could because this is one way to teach them. While playing, you are explaining them to do things and telling them what is that called and how to do it. Your kids will not notice that you are already teaching them and trying to test their creativity and logic thinking.