I wash all new things, be it for baby or adults. I do this for the following reasons
To wash off the finishing chemicals they put on clothes to make them look better. If clothes are being shipped from far away, they often use formaldehyde to prevent mildew growing on the clothes.
To remove excess dyes in the fabric (babies are especially sensitive to these reasons)
To wash in case someone else had already bought, used, and returned them (putting them back on the store shelves with ??? bacteria on them). It happens! Read a study once where they took new clothes and had microbiologists test them. They found all manner of human bacteria, from sweat to yeast to FECAL matter, on some of the ''brand new'' clothes..(which had been retagged and reshelved for sale) after people returned them to the store. All invisible to the naked eye and the clothes looked spanking new. You just never know...
That's all I need to know to get me washing! lol