With kids clothes I would do lots as what a child wears is at the parents discretion but as kids grow they are pickier and I think you would do better either pairing up outfits = shirt/pants, shirt/skirt, or just listing separately because if you are listing as a lot thus pricing as a lot and the buyer only wants 1 piece out of the lot they will not bid on it as they are not going to pay the price you want for all clothes. Just my opinion but it seems to always depend on what you are selling. Tshirts - list as a group, coats - list separately, etc. Run a search on items for the age bracket you are selling in and see what is selling and pricing to get an idea of what you should/should not spend your time on.