Every lens has advantages and disadvantages.

Advantages of the 50mm f/1.8 compared to the 18-55:

1. Great optical quality

2. It will give you much more depth of field control

Disadvantages:

1. The autofocus is painfully slow

2. It's a fixed focal length (it takes more time to move yourself than to zoom)

3. 50mm on a crop sensor is a little too tight, taking a group photo will be difficult or impossible in a small room

Basically the slower auto-focus and the need to position yourself (and sometimes your subject) rather than zoom will slow you down (or really teach you how to prepare and plan ahead), in exchange for this you get amazing image quality and DOF

So, it all comes down to what you plan on doing, for posed portraits the 50mm is better is just about every way, for taking shots or running children the 18-55 is better.

I have the 50mm f/1.8 and for my usage it's not a good fit, it mostly makes me wish I bought a 30mm or 35mm with a faster auto focus instead - but it is the cheapest way to experience what a fast lens can do and really see what you can get from a DSLR with a good lens that you can never get close to with a point and shoot.

Every lens has advantages and disadvantages.

Advantages of the 50mm f/1.8 compared to the 18-55:

1. Great optical quality

2. It will give you much more depth of field control

Disadvantages:

1. The autofocus is painfully slow

2. It's a fixed focal length (it takes more time to move yourself than to zoom)

3. 50mm on a crop sensor is a little too tight, taking a group photo will be difficult or impossible in a small room

Basically the slower auto-focus and the need to position yourself (and sometimes your subject) rather than zoom will slow you down (or really teach you how to prepare and plan ahead), in exchange for this you get amazing image quality (compared to consumer zooms, the more expensive lenses tend to be better) and DOF

So, it all comes down to what you plan on doing, for posed portraits the 50mm is better is just about every way, for taking shots or running children the 18-55 is better.

Note: the Canon EF 40mm f/2.8 STM is just a little more expensive than the 50mm, it got some great reviews and should solve the main problems of the 50mm f/1.8 (the old autofocus and that it's a little too long on a crop sensor) - but I've never used one myself so I can't really tell you how it works

I have the 50mm f/1.8 and for my usage it's not a good fit, it mostly makes me wish I bought a 30mm or 35mm with a faster auto focus instead - but it is the cheapest way to experience what a fast lens can do and really see what you can get from a DSLR with a good lens that you can never get close to with a point and shoot.