Comment This is another REALLY important cost (Score 1) 734
FATCA, the new rules meant to catch Americans hiding income offshore is forcing all manner of foreign financial institutions to register and report to the IRS. So your local bank in Belgium will likely decide it's not worth the hassle to deal with the forms and reporting for a US Citizen. They might not all have caught on to this, and if they don't have a parent company that does business with the US they might not bother, but certainly the laws are only going to get worse. So you granting them US Citizenship WILL make it harder for them to open a bank account, get a credit card or take out a loan. You really should consider that as well.
Of course they're not going after something that will actually result in real income like carried interest for the truly well heeled. But mess with your kids' lives as collateral damage? Absolutely.
I'm an American and I think it's the best place for me to live, but Belgium is sure nice to. But it'll harder to enjoy the great frites if you have the IRS spector haunting you.