Well, children at weddings is a sometimes controversial subject - but really, there is no right or wrong - it's all down to your own personal choice.
Personally I love children at weddings, they are such an important part of a family and add so much to the excitement of the day. Yes, you do sometimes end up with crying or talking at the wrong moment - but if you invited them, you just have to go with the flow on that one. On the other hand they can be adorable, amazing and beautiful all at the same time and can play such a big part in the whole event...
Don't forget - if you invite tinies, or even teenagers, give them something to do. A goody bag waiting on their seat full of lots of interesting things to do always goes down well. For teenagers, a private corner with a DVD player & movies or an xbox is a better idea - they will sing your praises forever more!
If you struggle with ideas to entertain them, nominate a friend to come up with a plan - that's what your bridesmaids and groomsmen are for!