I appreciate that I'm coming into this thread a bit late, but I have only just discovered it!
Obviously I would recommend going for it; it is a great lifestyle and very family-friendly. There is a whole mass of evidence that supports positive benefits for children and none, other than prejudiced statements from those who have no knowledge of Naturism, against it.
o2binsxm.com/childrenandsocialnudity.htm
Having said that, if your children are approaching or passing through puberty that is not a good time to introduce them to the lifestyle, although some will take to it even then. Prior to that most children take to it like a duck to water - a lot depends on how you have brought them up. Reluctance to be naked when it is comfortable to be so, is a taught behaviour; it is certainly not instinctive. For that reason the younger the child, the more natural it is to them.
Never force a child to take part. No reasonable Naturist will mind if your children do not undress, especially if they know it is their first time. The only possible exception to this would be in the pool at a Naturist club where the wearing of costumes is usually banned - this is for hygiene reasons - yes, costumes are less hygienic and cause the pool filters to need more frequent cleaning!
To those who claim to have had dodgy experiences I ask; are you sure you were experiencing true Naturism? I'm sorry to say we can do nothing about swingers clubs masquerading as 'Naturist' as there is no copyright on the name. Most people who describe themselves as Naturists are genuine, so hopefully this applies to your new guy.