"Will ISKCON accept people this young?"
Oh, yes, we, younger, even younger. Even one child is within the womb of his mother, we can teach. It is so nice thing.
The instance is Prahlāda Mahārāja. Prahlāda Mahārāja, when he was in his womb of his mother, one saintly sage taught his mother about Kṛṣṇa consciousness, and the child became Kṛṣṇa conscious from the womb of his mother. So we can teach even in the womb of the mother because it is spiritual, it is not material. No material condition can check this teaching. Ahaituky apratihatā (SB 1.2.6).
That is the highest perfectional system of religion, which is unchecked and develops love of Godhead. That is first-class religion, not under any condition. Ahaituky apratihatā. Apratihatā without being checked.
Kṛṣṇa consciousness is not such thing that because one is child, he cannot learn; because one is blind, he cannot learn; because one is poor, therefore he cannot . . . because one is rich . . . no condition. Anyone, simply he must be a living entity, that's all. He must not be a dead stone. If he has got life, he can learn Kṛṣṇa consciousness. It is so simple and so nice.