My kids did pleasure themselves all the time sometimes alone and many times together.Telling them no does not stop them from exploring.Specially when one is at work and the other parent is busy preparing meals.
Haha. You're user name is nakednow. You're seriously worried about your kids exploring. It is what it is. One can never successfully stop what people are born to do. To them it's normal. Let them decide in time wether to continue.
In your day yes it may of been ok to do but in modern day if someone happened to find out and report it to social services the parent could lose there kids over it, you have to look at the bigger picture of the modern world not just back 40 year ago!
In the original question the only cause for intervention would be if one sibling forced the other to masturbate with them against their wishes.The abuse happens when one forces the other to do something the other does not want.
Watching pornography is the problem in this situation because pornography is showing a unrealistic view of the body.It gives the impression one needs a body with this type of length or this large of a breast to be beautiful.
If siblings masturbate together not so much two brothers or two sisters but specially boy an girl and the go to school and tell friends as you said and that conversation gets over heard by a teacher and taken into the wrong context and gets reported child services would have a duty to step in and talk to the parents about what's going on, it has nothing to do with abuse its about child welfare.
Any child welfare teams whether it be in the US, or UK or any other country have a duty to follow up on reports once they receive them specially with all the bad press reports they are getting these days over not investigating cases thoroughly.
Each case is followed up whether it is false or true by protective services.In this particular instance the children did no wrong.Protective services would find that out during their investigation.
Your concern here is that it might escalate to something more so you want them apart.If this instance they were both females or both males you want them to be apart just in case it escalates to touching.
I also think you would find that if for instance they found out in was brother and sister masturbating together it would be followed up.
I don't know about in the US but here in the UK children over a certain age have to have separate bedrooms boys can share a room girls can share a room, if for any reason say you had a 10 year old boy an a 12 year old girl or vise verser sharing the same room an child services found out they would then come out to investigate.
I'm not saying keep them apart I'm simply saying parents need to explain that masturbation is a private thing that should be done alone specially if it became knowledge that brother and sister was doing it together.
I forgot to mention age of consent and it varies from country to country.Some are as low as 13 most average is sixteen.
When I was talking about every case is investigated I forgot to mention that it was in the USA.So the lowest age of consent in USA in 2017 is 16.
So to make light of this scenario it depends where you are and what local statutes are in regards to if masturbation is considered as sex.Sex in most cases are when actual intercourse takes place.
So to you blankcanvass I apologize if I sounded to harsh.So as a parent anywhere if you feel it is not right for your kids to be masturbating together it is your choice whether to permit it or not.It is your house if you think that it could escalate to something more then act accordingly.
It is the parents decision if they let it go on in there house holds but those parents that do allow it also have to realise there could be consequences if it did happen to get found out.
I'm not saying kids need to be locked in there separate rooms they just need to be educated on the wrongs and rights of masturbation and if a parent does let them masturbate together then the parent needs to tell them to keep it between themselves as some people may see it as wrong.
Back 30 to 40 year ago masturbation wouldn't of been such an open subject between kids like it is now so conversations wouldn't of been heard like now days.