If it's an x-deal as they call it for portfolio of an upcoming photographer. I guess it's fine for as long as he/she will not use the photos for media marketing such as product endorsement and asking it for free while he/she gets paid for that without informing the subject about a deal, then that's a No. Also the parents should clarify if the naked shots are not "too sexual" for I believe naked shots for children are quite a trend when it comes to newborn and child photography even on maternity shoots.
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