If their's one thing to be certain of, kids are going to grow, and so everything you've bought them you'll have to keep buying again and again in a bigger size.
For this reason, Encina Bicycle Center and Clayton Bicycle Center offer a trade-in program to keep the kids riding their bikes and minimize the impact on your wallet. Purchase your child's first (or second or third) bike knowing that when they outgrow it, you will get 50% off the purchase price of the bike credited toward a new bike.
For example, it is time to buy Johnny his first bike. He loves the 12" Specialized Hotrock Coaster that has a retail price of $200. When Johnny outgrows the 12" bike, simply bring it to the store and receive a $100 credit toward a new 16" Specialized Hotrock Coaster and only pay $120 plus tax (16" Hotrock Coaster retail $220 - $100 credit = $120 + tax)
It's that simple, but keep in mind that just like everything in life, there are some restrictions.