If you have bought a beautiful dress for your child for a special occasion then you may want to find some accessories to match. Some shops will sell matching accessories for dresses but some do not and if a dress is in the sale, then you almost certainly will not be able to find the matching accessories too.
If you have chosen a dress based on a specific colour for example, then you need to make sure that the accessories are either a totally different colour that still goes or they are the same shade as the dress. For example, there are many different shades of blue and having two different ones may not look as good.
If you are shopping for hair accessories then you can browse hundreds of them online from a number of stores, but if at all possible, try and have a look at them in store. If the accessories are from an auction site then be sure to check the quality and check if you can return the item free of charge if you are not completely satisfied.