It really depends on the age of the siblings.
Younger siblings would definitely want a party bag, whereas older siblings probably from the age of 10 upwards wouldn’t really be that bothered.
If the birthday child has older siblings, perhaps it would be a good idea to get them to make up the party bags or to help you make them up. This way they will feel included and chuffed that they have created them. You could get them to decorate plain paper party bags, design a ‘Thank You’ gift tag for the bags, or put all the party bag fillers into the bags for you.
All party guests should really get a party bag gift, regardless of whether they are siblings or even the birthday child themselves. I know it seems a bit strange to arrange party bags for your own kids, but why not if it makes them happy!
For siblings of party guests, well this is a different story. Yes they would need a party bag if they are actually invited to the party, but not if they have come along uninvited or have come to pick up their brother or sister from the party.
It can be quite tricky when a younger sibling happens to be around when the party bags are being given out to the party guests. Some of them get quite upset and it’s a hard task for parents to calm them down and tell them they can’t have one. This is why it’s probably a good idea to have some sweets at hand or a small token gift such as bubble mixture or a balloon.
Of course if you have any party bags going spare, you could always give them one if it’s suitable for them, but that’s entirely upto you.