After I got home, my kids grabbed my duffle bag and asked what I got them. My kids are 9 (boy), 8 (girl), and 5 (girl) with the best manners ever. =) I let them take what they wanted to play with and asked them to help me review it.
All three of them gravitated to the Tinkertoys by K’nex.
According to the web site, children benefit by
• Improved motor skills, such as hand-eye coordination
• The joy of creating something all their own
• A tangible product of their imagination
• Social skills as they build with siblings and friends
• Language skills as they explain their creations
I can tell you especially with my Kindergartener, she is gaining a knowledge of colors, shapes, spatial awareness, construction, engineering, and the satisfaction of creating a tangible object. She loves to make flowers.
My 9 year old son who wanted me to write that he will be 10 in December, likes to build anything with them. He is gaining an understanding of engineering. His favorite thing was to build was a chair. We tested how much weight it would hold with my daughters’ dolls. The chair held an 18 inch doll. 
My 8 year old said it makes you think a lot and get creative to make anything. She created this by copying an idea that was on the instructions. I love the fact she made it her own. This idea teaches that it is okay to go off the block and be creative.
I would highly recommend buying Tinkertoys by K’nex. You can purchase at any toy store. The price ranges from $19.99 to $27.00 depending on the retail store.
I was given a Tinkertoy by Knex. My opinions are my own though.
