Q. Is it totally uncool to bring my older child to a birthday party that my 3-year-old was invited to?
A. Totally -- unless you've cleared it with the host first. After all, the mom in charge has prepared the cupcakes and Pin the Tail on the Donkey for six 3-year-olds, not a bunch of big brothers and sisters who could quite easily (and quickly) eat their way through the buffet and then (mindlessly, innocently) wreak havoc on what was supposed to have been an intimate preschool affair.
If the host says bring him along, be prepared to keep your older child out of the way of the festivities -- no letting him slay the piñata and snatch a big-kid share of candy. And if the party is at one of those pay-and-play places, make sure you get your wallet out and pay his way. But don't be very surprised -- or upset -- if the host tells you politely, "No siblings welcome."