This hobby that i would like to talk about quite consuming money, where considered by some that it's a waste of money, but for me it's give me satisfaction where everything's need to build from nothing to a things that move.
Most people called it AFOL, where it's refer to LEGO fan or hobbyist. The world of LEGO are full of possibility and imagination where you able to build up somethings that from reality and even build somethings that out of the box.
Why is it expensive
It's because sometime we need some parts specially from one edition of LEGO set while can't be found at another set of collections.
What are LEGOS?
Legos consists of colorful interlocking plastic bricks, an array of gears, mini characters and various other parts. LEGO bricks can be assembled to construct vehicles, buildings, people, bridges, and even working robots. Anything constructed can then be taken apart again, and the pieces used to make other objects. LEGOs are enjoyed by "kids" of all ages. You will find that if you played with LEGOs as a kid, you will be excited to introduce your child to them.
Why are LEGOS a good hobby?
It is a great past time for kids and it can be turned into a great hobby. It inspires imagination, and creativity and it helps improve fine motor skills. LEGOs has a set to go with just about any interest your child may have. There are thousands of sets on the market so you have the option to create a theme and add on to it, or just pick and choose as you go along. 
LEGO sets include: town and city, space, robots, pirates, Vikings, castles, knights, dinosaurs, holiday locations, undersea exploration, the wild west, the Arctic, airports, miners, Star Wars, Batman, SpongeBob, Avatar: The Last Airbender, Harry Potter, Bionicle, Indiana Jones, Exo-Force and Speed Racer.
There are sets available for all age groups so you can introduce your young ones early to the creative play LEGOs offer. The have larger bricks for toddlers that will teach them dexterity. The smaller bricks will keep the attention of preschoolers on up for long periods of time. They even have pastel colors for girls.
Some kids like to keep the LEGOs built and others like to break them apart and build new things by combining multiple sets. The one thing that all kids have in common is that they love to show off what they made, so be sure to have a secure place to display their masterpieces. LEGOs are very durable and quite generic in design. You will find that they last forever and old and new alike with work together. So if grand mom has some stored in the attic be sure to pull them back out again.
Storing LEGO Sets
I can tell you from experience that you can accumulate a lot of LEGOs quickly and the pieces can be very small. My suggestions would be that If your child opts to keep them built then the best thing to do is to build shelves in their room or purchase a bookcase to house them. If you purchase a bookcase consider something with glass on the front to keep them from getting full of dust. This will keep them on display for everyone to see but will also keep them safe.
If your child enjoys the excitement of putting them together but then likes to take them apart and make something new then you will need storage. You can store them in original boxes, plastic containers, zip lock bags or plastic drawers. They can be organized unsorted with all pieces mixed together or you can sort by set, color, size, category or part. Don't try to develop the perfect sorting and storage system with the purchase of your first set, wait until the collection grows.
I found it best to keep them in the original packaging with the instructions. I can guarantee you that at some point they will want to go back and build it the original way again and without the instructions it will be very difficult. If you don't store them in the original box then you should consider cutting the small pictures from the original boxes to use to identify what is in your collection and keep the instructions.
There are also LEGO tables that are available for around $250 - $300 so that your child has their own space for building. Many come with storage as well.
For detailed tips on sorting and organizing LEGOs check out these sites:
The best option for you will depend on how many pieces you have, how your child likes to build and your space constraints.