"Can I Bring His Little Sister?"
The text every host gets after ordering the cake, and the one line on the invitation that prevents it.
Every parent hosting a kids' party eventually gets this text:
Is it okay if I bring his little sister?
It's a reasonable question. It's also the question most likely to blow up your headcount, your budget, and your venue's capacity — and it almost always arrives after you've ordered the cake.
The fix is to answer it on the invitation, before anyone has to ask.
Pick a position and state it
You have three realistic options.
Siblings welcome
Siblings welcome — just include them in your RSVP count.
Invited child only
Our venue caps us at 12 kids, so this one's just for the invited guests.
Ask me
Got a sibling who'd like to come? Mention it in your RSVP and we'll sort it.
Give a reason when the answer is no
This is the difference between a line that lands well and one that doesn't.
"Invited guests only" sounds like a rule about someone's child. "The venue caps us at 12 kids" is a fact about a room.
Nobody argues with a room.
You don't owe anyone a detailed explanation. A short concrete reason — the venue's limit, the size of the table, the number of craft kits — does the work, because it isn't about their family.
While you're at it: say whether you're staying
Siblings and drop-off are the same underlying question. Who exactly is coming, and are the grown-ups staying?
If you want parents to stay:
Parents welcome to stay — there's coffee.
If you're happy with drop-off:
Drop-off is fine for ages 5+. We'll be here the whole time.
Getting this wrong in either direction is uncomfortable. Ten unexpected adults is a catering problem. Ten unexpected drop-offs is a supervision problem.
Count kids and grown-ups separately
"Four of us!" doesn't tell you what you need.
Four kids means four party bags, four chairs at the craft table, four slices. Two kids and two adults is a completely different shopping list.
Ask for the two numbers separately and the ambiguity disappears.
How CubbyCard handles this
The RSVP asks for child count and grown-up count as separate fields, so you get actual numbers instead of "us!" And you can put your sibling line directly in the invitation wording, which means it's answered before the question gets asked.
One link, one place the answers live, and a headcount you can shop from.