Sponge baths are fine as well, but it's still advisable that you use a washcloth to wipe his body as well.
The thing about using a sponge instead of a washcloth is that sponges are excellent breeding grounds for bacteria and germs, so be sure to change the sponges frequently.
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http://www.babycenter.in/x1015318/how-do-i-give-my-baby-a-sponge-bath
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