I have never attended a wedding that was "adults only". That being said, I support the B&G in making their guest list and deciding that they will not invite children.
We don't know the B&G's reasons for not inviting kids (if indeed they're not). The Bride may have parents that have 15 siblings between them, all 4 of her grandparents are alive, she has 6 siblings (married), and both of her parents are remarried. That would be 50 people just in that group. Perhaps they have 20 friends between them, half of whom are married. We're now up to 80 invites not counting the groom's side. If their venue and budget only allows them 125 people, they really are stuck between a rock and hard place. They may have made a unilateral decision to not invite any children including their (adult) first cousins.*
If OP's kids aren't invited I hope her DH takes into consideration what the actual logistics are with the invites. If the scenario is one like I typed above, I would hope that DH would go to his brothers wedding.
*I took the numbers I used from my DIL's actual family. Starting to plan that wedding was a nightmare. Then DS joined the Air Force, and they got married last month by a JOP with only parents and siblings present. Much simpler and no feelings were hurt. 
When I got married, I stopped the "family" circle of invitations at my aunts and uncles, and didn't invite any of my cousins (mostly adults by then). There were several reasons for this, including but not limited to the fact that I've never been close to any of them (partly due to age differences), and the fact that I really don't care to associate with some of them. And I told my dad that he
would call one of my uncles (Dad's brother), and
would inform him and my aunt (his wife) that they were not to bring anyone not listed on the invitation. I might not have gotten away with that if Mom hadn't supported me 100%, but she did.
Most likely that was rude, but in my defense, I knew from long experience that that particular branch of the family had a habit of bringing their children, the childrens' SOs, and the grandchildren - some of whom were not over-endowed with manners. No matter the occasion or who was or was not listed on the invitation. And I was not, absolutely
not, going to deal with that on my wedding day. Especially because there was just enough room for the invited guests for the ceremony portion - the reception was more spread out through the venue, so there was plenty of space for people to mingle and talk and such. I don't know - was it actually rude to have that point made to them if it was based on actual past experience? If so, how long a stay in eHell is appropriate?
