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The U.S. requires immigrants applying for naturalization to renounce their previous citizenship. Customarily, parents seeking naturalization also renounce, on behalf of their children, their children's previous citizenship.

Are you saying that Indonesia wouldn't require (or even allow) the same?

I'm saying that Indonesian law is irrelevant to the question of U.S. citizenship. From the U.S. State Department:

Parents cannot renounce U.S. citizenship on behalf of their minor children. Before an oath of renunciation will be administered under Section 349(a)(5) of the INA, a person under the age of eighteen must convince a U.S. diplomatic or consular officer that he/she fully understands the nature and consequences of the oath of renunciation, is not subject to duress or undue influence, and is voluntarily seeking to renounce his/her U.S. citizenship.