How early should a kids' birthday invitation go out?
One to two weeks gives parents room to rearrange Saturday plans without leaving you a long gap of uncertainty. Put a reply-by date on the page and count heads a day or two before, rather than the night before, when the cake is already paid for.
Does the wording change much with the child's age?
What changes is the content, not the tone. Three-year-olds mean stay-and-go parties and a short running order. Older children mean drop-off, a longer window, and a real gift question. Write for the age the party is actually for.
How do I ask about allergies without listing every child's needs?
State what you are serving, what the cake is free from, and invite a note with the reply. You get what you need without turning an invitation into a medical circular, and nobody's diagnosis ends up displayed to the class group.
Can I change the pick-up time after the invitations are out?
Yes, and it is the strongest argument for an invitation that lives at a link. Edit the time, save it, and the page everyone already has shows the new one. No reprint, and no apology message sent at eleven at night.
Do the other parents need an account to reply?
No. They open the link, tap yes, say who is coming, and go. Anything you need beyond that, a sibling question or a dietary note, arrives with the reply and lands on your list with a name against it.