It's a good idea to encourage your children to clean up their toys. It will teach them to take care of their things and become organized. If they start playing with a toy and decide they want to move on to something else, remind them to clean up first so you don't end up with toys all over the floor. Easier said than done right? This isn't always easy, especially if you have more than one child. Most young children have a short attention span, so they quickly go from one activity to another.
To help your children learn to clean up their toys you should be their role model. If your children see you picking up toys and putting them away they will want to do the same. I'm constantly picking up toys in our house, but our children have started doing it too. Our five year old is a very good cleaner. If we ask her to clean up her toys she does it and sometimes we don't have to ask. If I comment about the mess she'll start cleaning up. Our three year old usually does what her older sister does. While I'm cleaning up the toys I explain to them what I'm doing. For example, our three year old has a habit of colouring with washable markers and leaving the lids off of them when she's done. I always remind her to remember to put the lids back on them because they'll dry out and won't be good anymore. We usually sing a cleanup song while we're cleaning up to make it more enjoyable. It's also a good idea to give them a warning ahead of time. For example, you can say something like "five more minutes and then it's time to clean up." This way they're prepared and they know what you expect from them.