My husband and I had only been married 8 years when we renewed ours. When we had our "proper" wedding we already had our son but not our daughter. When our daughter was about 6 she seen our wedding photos and when she wasn't on any of them she asked why. I told her she hadn't been born so she said it wasn't fair she was never around when anything exciting happened. At about the same time a few of her friends parents split up and she got herself quite worried that we were going to do the same. We were going away for Christmas to a cottage in the Yorkshire Dales and we arranged with the Vicar of a tiny local church in the area to renew our vows. We kept it a secret from the kids but bought them special outfits, a present each (because they were going to be our special little best man and bridesmaid) and also got a cake with this written on. There was only my husband and I and the two kids in this beautiful church on Christmas Eve, renewing our vows in front of our children. It was really lovely and we all enjoyed it very much although my husbands friends even now still say they can't believe he got married a second time to the same person!
I think its lovely to renew your wedding vows no matter how long or short a time you have been married.