Grammar Police - Please Help

Run, Bounce, Jump, and Play
at the 4th Birthday Celebration
for Johnny and Stanley

or

Run, Bounce, Jump, and Play
Johnny and Stanley invite you to
Celebrate their 4th Birthdays

Less awkward wording also eliminates the punctuation issue. :-)

If the two boys are twins, and there is one birthday, I believe it should be Johnny and Stanley's 4th birthday. Two boys, one birthday. Then you could say "It is Johnny and Stanley's 4th Birthday".

If there are two birthdays (Johnny's is on the 6th, Stanley's is on the 14th but they're having a joint party because they're both turning 4 and we're sharing the cost of hiring a clown and renting a venue, for example), it should be Johnny's and Stanley's 4th birthdays. Two boys, two birthdays.

And I guess in that event, you shouldn't say "it is", but rather something like "come celebrate", since "it" is not one birthday. "Come Celebrate Johnny's and Stanley's 4th Birthdays!"

That's my two (or is it four, or perhaps eight, in this case?) cents.

Johnny and Stanley invite you to
Run, Bounce, Jump & Play
Because they're sharing this 4th Birthday!

(I'm a master at the workaround!)

ETA: FWIW, I believe only the second name gets an apostrophe!)
Also: birthday, not birthdays.

I think you put an apostrophe after the second name if they are sharing the object: Johnny and Stanley's Birthday Celebration
Hope your son has an awesome birthday!

Well, the technical answer...the apostrophe s shows possession. If you write "Johnny and Stanley's...whatever" it means that the two share possession of the whatever. If you add an s to each, it shows that they each have one of the whatevers. If it were twins, it would be clear that Johnny and Stanley's birthday is appropriate- in a very literal way, they share a birthday. In that case, it would also be appropriate for birthday to be singular, as possession is shared. You could write Johnny's and Stanley's 4th Birthdays and it would be correct, indicating that they each have a birthday that may not necessarily be the same day. If they are on different days, that would be most accurate but, in my opinion, that would be a bit awkward on the invitation.

Can you tweak the language?

Happy 4th Birthday to Johnny and Stanley

Let's Run, Bounce, Jump and Play

to celebrate this special day!

Best,
T. Y

Johnny and Stanley's

Birthday

Do they really call them "Johnny and Stanley?" Or John and Stan?

Jump, Play, Bounce and Run,
It's John and Stan's 4th birthday celebration!
Arrive at 2 for games, cake and juice,
We'll fill your kids with sugar and send them home with you!

;) Couldn't resist.

I like the workaround better, but if you go with your original, I believe it would be both names possessive, and plural birthday. :)

Happy birthday to the kiddos!

You can't be perfectly correct AND clever with this one. What AZneomom said about the shared possession is spot on, and I can't imagine a way to write that and keep it cute.

Also, while "it is" is formally correct for writing, it throws off the rhythm. "It's" would apply to a singular subject--birthday. And I don't like the use of the ampersand, unless this line will be written in bold and playful characters.

How about "It's for Johnny's and Stanley's 4th birthdays"? Does that keep the spirit?