Kids always seem to be getting more and more toys, and the situation can easily get out of control. They are also notorious for not picking up after themselves, and getting upset when they can't find the particular toy that they are looking for. There are a number of ways you can help to control the chaos. A rack shelving storage system and a bit of time spent organizing can really go a long way in helping to get things under control.
One of the first things you should do is get some rack shelving with bins. For smaller kids it is nice to have the open bins on angled shelves so they can easily see what is in each bin and reach what they would like. If you organize everything small into these bins and set up shelves for the larger toys, you can then label the places where each type of toy goes (either with pictures for smaller kids or words for bigger kids) so that it is obvious where everything belongs. Try to get the kids to put things away when they are done playing.
Bin Toy Organizer
If the amount of toys that the kids have is just too crazy and out of control, you can try sorting them out into groups of toys that you rotate. Every few months you can switch the toys that are out in the bins and shelves and it will be like they have all new toys. Most kids are happy to go along with this system since too many toys at once can be a bit overwhelming, and they tend to forget what all they have. You can store the toys that are out of rotation in closed bins in a closet or maybe on rack shelving in the basement.
There are a number of rack shelving systems out there that are meant just for kids. They are colorful and made with kid friendly designs so that they will look right in any toy room. However, you can also adapt any shelving that you have. Use colored baskets or bins to go with the decor of the room where the kids usually play and store their toys.