Being a mother of two children I think it is wrong. I couldn't afford to buy presents for both of my girls on each of their birthdays. It's ridiculous. Children need to learn. Yes one child will think 'why aren't I getting presents' and so on but you can prevent that from happening:
Get them involved.
If you're making a cake, get them to help you and tell them it is a surprise. Get them to help you put decorations up, write in cards and wrap presents. This will get them excited for their siblings birthday.
Let them help
Same as above, but let them help by maybe helping to open presents if there are a lot.
Is it just me who does not understand that point on wasting money to buy the other child a present just incase they get jealous? I think there are plenty of other ways to do this, such as the advice I gave above. I think if you involve them into things, don't leave them out - then I don't see the problem.
What do you think about this? Would you give your other children presents on another child's birthday just because they will get jealous??