I love finding unusual/bright/interesting kids clothes
Mini Mode/Boots do nice clothes and some dire stuff too.
Adams are trading online and again are a mix.
Tesco is good this season, Asda and Sainsburys not so much.
On ebay I use the search filters on the left and filter out anything blue or brown so I am left with interesting and unusual things. You can filter by brand as well which helps. (to filter out the worst offenders)
Here are some sample ebay searches for you:
3-6 + 6-9 months Girls
Boys 2-3 years
Boys age 18-24 months
Also if you want to win stuff on ebay, you need to watch it rather than bid straight away. I usually watch things which catch my eye, then go into My Ebay and look at each watched item to see if the seller has any other items I like (I usually try and win at least 2 items from each seller to keep postage down) so I might end up with loads of items to watch on ebay. Then every day I go and look at the items I have watched to see how long they have left, if they have less than a day left or I don't think I'll get on the PC in time to bid then I will bid then - I win a lot more when I bid at the last minute I possibly can than if I bid when I first see the item.
So if you want to shop quickly then sort the searches by "ending soonest" but if you are happy to play the watching and pouncing at the end game then sort the searches by "lowest price" I have left them sorted by "best match" which I think means the ones people have clicked on the most - so not the best way to sort it.
Hope that all makes sense