First and foremost, to be able to answer this, one must know the scientific name of the plant species that are commonly referred to as 'moonflowers'. Sometimes common names refer to multiple species which can make this question challenging to answer. In this case, I will make the assumption that 'moonflower' refers to the species known as Datura alba. It is rather important that the client confirm this before accepting this response.

Next, the references that I checked including a textbook on "Poisonous Plants of the United States and Canada" by J. M. Kingsbury (1964) states that there are more than a dozen plants in the Datura genus of plants and while he did not list this particular species, he does says that species in this genus have been known as poisonous plants since ancient times. In addition to humans, ostrich, chickens, horses, sheep, hogs and mules (quick search added dogs and cats to this list) have ingested fresh leaves or tissues of this plant and have displays symptoms of poisoning including mortality. It is important to note that must poisonings are due to feed contamination and that livestock find these plant tissues to be evil smelling and will only eat it if forced to. Supporting documentation found at https://en.wikipedia.org/wiki/Datura

Finally, I have to quote a passage directly from this Kingsbury reference "This plant is unusual in that human poisonings are more commonly reported in recent literature than are animals poisonings. The large, showy flowers and spiny capsules especially intrigue children and lead to poisonings" from ingestion of nectar or seeds. The paragraph further goes on the mention that "tea" and decoctions deliberately used for hallucinogenic effects are dangerous and account for many cases of poisonings.  

Finally, our conclusion is to say "absolutely no" to tea, "no" to seeds, and to Datura in home gardens and landscapes--especially if you have any reservations or concerns about potential pet and/or children toxicity.  

"First and foremost, to be able to answer this, one must know the scientific name of the plant species that are commonly referred to as 'moonflowers'. … I will make the assumption that 'moonflower' refers to the species known as Datura alba. It is rather important that the client confirm this before accepting this response."

Thanks for allowing me an opportunity to more clearly address this question. Datura 'Alba' was how the reference to the plant I have seen advertised as moonflower. The quotations indicate that this was a cultivar not a species- my mistake! The species is Datura metel. My response was specific to the Datura genus not a species, because I was not sure of the species. The best source to seek a species identification would be the source of the seed.

So now that my mistake is out there, let's continue with the discussion. According to Wikipedia, "Datura inoxia is quite similar to Datura metel to the point of being confused with it in early scientific literature." Furthermore, "Datura inoxia differs from D. stramonium, D. metel & D.fastuosa in having about 7 to 10 secondary veins on either side of the midrib of the leaf which anastomose by arches at about 1 to 3 mm. from the margin."   Well only after looking up that medical term "anastomose", can I say that this description does match up well with the leaves that were in the second picture that you sent.  So you are right, this moonflower does appear to be Datura inoxia, not Datura metel 'Alba'.  Still the discussion about the toxicity of all plants in this genus applies. 

The one part of your question that I neglected to address was weather this is a weed or a decoration.  This plant does have weedy characteristics, but according to the Walla Walla County Noxious Weed Board, Datura species are not considered to be noxious weeds that need to be eradicated or control in your county nor are they listed as noxious weeds in the state of Washington. 

I hope this response better addresses your question.