"An infant is not able to have faith."

I believe the thought process revealed in the above statement is the thought process of the old man. It is, in other words, an adamic thought. A thought that doesn't arise from Christ in us, but rather from our old sinful nature. I do not believe that there is a single verse of scripture that teaches that faith is impossible due to lack of intellectual capacity. In fact, the Bible teaches the opposite, that God delights himself in calling those that are not intellectually brilliant or high achievers by human standards.

1Co 1:26-29  For consider your calling, brothers: not many of you were wise according to worldly standards, not many were powerful, not many were of noble birth. But God chose what is foolish in the world to shame the wise; God chose what is weak in the world to shame the strong; God chose what is low and despised in the world, even things that are not, to bring to nothing things that are, so that no human being might boast in the presence of God.

The Bible takes away even the smallest little bit of self-merit that our sinfulness so avidly tries to grasp. We cannot even credit our intellectual ability as having anything to do with our salvation. It is God's rightful prerogative to get all the glory for our salvation so that that we are left with no right to boast nor congratulate ourselves.

Initial salvation and conversion (which includes what we commonly call justification) is not due to any work in the one being saved, but rather to the work of God. Consider who is the mover and author of salvation in the following verses:

1Co 3:6  I planted, Apollos watered, but God gave the growth.
2Co 4:6  For God, who said, "Let light shine out of darkness," has shone in our hearts to give the light of the knowledge of the glory of God in the face of Jesus Christ.
1Pe 1:23  since you have been born again, not of perishable seed but of imperishable, through the living and abiding word of God;
Joh 1:12  But to all who did receive him, who believed in his name, he gave the right to become children of God, who were born, not of blood nor of the will of the flesh nor of the will of man, but of God.
Joh 3:5  Jesus answered, "Truly, truly, I say to you, unless one is born of water and the Spirit, he cannot enter the kingdom of God. That which is born of the flesh is flesh, and that which is born of the Spirit is spirit.
Eph 2:4  But God, being rich in mercy, because of the great love with which he loved us, even when we were dead in our trespasses, made us alive together with Christ--by grace you have been saved--
Tit 3:5  he saved us, not because of works done by us in righteousness, but according to his own mercy, by the washing of regeneration and renewal of the Holy Spirit, whom he poured out on us richly through Jesus Christ our Savior,

Now this shows that faith is something for which God, not man, provides the preconditions. God, of course, does not believe for us. It is our duty to believe. However he is the complete enabler of our faith. A faith that does not depend on our natural abilities, but rather his divine working.

The real question is not, "How can infants have faith?" but rather, "How can anyone have faith?" If you maintain that infants cannot have faith because they lack some natural ability, you are in effect saying that you, because of some natural ability you possess, are more able to come to God! But what does God say about natural ability?

1Co 2:14  The natural person does not accept the things of the Spirit of God, for they are folly to him, and he is not able to understand them because they are spiritually discerned.

How can it be less impossible for an infant to be saved that you? Impossible is impossible. There is no such thing as more impossible.

In fact Christ explicitly teaches that it is more possible for children to have faith. Why? Because of some natural ability in them? No! By nature it is just as impossible for them to be saved as you. The reason is that God loves revealing himself to those of less natural ability.

Mat 19:14  but Jesus said, "Let the little children come to me and do not hinder them, for to such belongs the kingdom of heaven."

Mat 11:25  At that time Jesus declared, "I thank you, Father, Lord of heaven and earth, that you have hidden these things from the wise and understanding and revealed them to little children;

Please remember that God's ways are higher than our ways and his thoughts higher than our thoughts. If God wishes to work faith into a single-celled human zygote, he can, and will, and most certainly has.

Luk 1:15  for he (John the Baptists) will be great before the Lord... he will be filled with the Holy Spirit, even from his mother's womb.

In your heart there is a purpose.
A purpose that you have for us.
Even if I can't see my way
may you grant me the faith to stay,
always, forever in your hand.

Trusting is at times confusing,
unsure, unstable, bemusing.
You gave to me the down payment.
May I have faith to fulfillment,
and forever be in your hand.

Lonely but you are still with me.
Entangled but completely free.
May I realize that all my dreams
are found flowing within your streams
of love and mercy in your hand.

For your promises I thank you.
Again to realize anew
the truth under reality!
Living not confined to feelings
is to be at peace in your hand.