Not only do you have to get the colour and type of bike right you will need to accurately judge the right size of bike without giving away the game that you went and picked the bike, not good old St Nicholas.Bike SizingChildren's bikes generally fall into one of a number of different size categories which are based on their size and age. The age is only a rough guide, as we all know; there are always children who are taller or shorter than the average.The following list should give you a good guide on what size bike you should be purchasing for your son or daughter this Christmas;- 12" Wheel Cycles - Suitable for ages 2½ to 4 - 14" Wheel Cycles - Suitable for ages 3 to 5 - 16" Wheel Cycles - Suitable for ages 5 to 7 - 20" Wheel Cycles - Suitable for ages 7 to 9 - 24" Wheel Cycles - Suitable for ages 9 to 11 - 26"+ Wheel Cycles - Suitable for ages 11+Bikes in the 12" and 14" wheels categories are generally fitted with stabilisers only if your child excels at riding their bike these can be removed. From 16" wheels and upwards you will find that these will not come fitted as standard as your child will normally have learnt to ride without the assistance by this age.If you are buying one of the 12"or 14" wheeled bikes be very careful and choosey about your purchase. A number of these bikes are made from lesser quality plastic parts that may break easily and be difficult to replace. Always check with the store first and enquire about these before rushing into a purchase.Popular Types of BikesBMX - A BMX (named after Bicycle Motor Cross) is a single speed, usually 20" wheeled bike. Very popular in their cheaper versions with younger children, these bikes have now grown into a cult scene with stars, such as Matt Hoffman, making BMXing a hugely popular sport. A cheap BMX is great for a younger child, but should your boy, or indeed girl, wish to start riding these bikes as intended make sure you invest in a good quality name that is built to take some punishment. Some good names to look out for are WeThePeople and Mongoose who both make excellent, but affordable BMX's.Mountain Bike - Mountain Bikes, like BMX's come in both cheap and quality versions. A cheap mountain bike will offer your child an introduction to gearing and make the bike more versatile however really shouldn't be used for any off road riding for safety reasons. After this mountain bikes can fall into one of a under of sub categories such as dirt jumping, all mountain, hard tail, full suspension and generally the most expensive of all; downhill.