Westminster Larger Catechism:

Question 165: WHAT is Baptism?
Answer 165: Baptism is a sacrament of the New Testament, wherein Christ hath ordained the washing with water in the name of the Father, and of the Son, and of the Holy Ghost, to be a sign and seal . . .
  of ingrafting into himself,
  of remission of sins by his blood,
  and regeneration by his Spirit;
  of adoption, and
  resurrection unto everlasting life;
and whereby the parties baptized are solemnly admitted into the visible church, and enter into an open and professed engagement to be wholly and only the Lord's.

Question 166: Unto WHOM is Baptism to be administered?
Answer 166: Baptism is not to be administered to any that are out of the visible church, and so strangers from the covenant of promise, till they profess their faith in Christ, and obedience to him, but infants descending from parents, either both, or but one of them, professing faith in Christ, and obedience to him, are in that respect within the covenant, and to be baptized.

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I was sprinkled when I was a child!

(Charles Spurgeon)

Some tell us that in baptism, by which they mean infant sprinkling as a rule - they regenerate and make members of Christ, children of God, and inheritors of the Kingdom of Heaven!

But those who are sprinkled as infants are no better than other people! They grow up in just the same way as others. The whole ceremony is useless and worse than that, for it is clean contrary to the example and teaching of the Lord Jesus Christ! No aqueous applications, no outward ceremonies can ever affect the heart!

The fact is, baptismal regeneration is a lie - a wicked invention of Popery, without the slightest warrant in the Word of God! Not one has ever been born-again in baptism, nor ever can be!

We are told that infants can be regenerated by baptism - and we have seen these regenerated infants develop into what, to our minds, was nothing more than baptized heathen, washed to deeper stains!

I was sprinkled when I was a child - but I know that I was not thereby made a member of Christ, a child of God and an inheritor of the Kingdom of Heaven! I know that nothing of the kind took place in me - but that, as soon as I could, I went into sin and continued in it!

I was not born-again, I am sure, until I was about fifteen years of age, when the Lord brought salvation to my soul through the regenerating work of the Holy Spirit - and so I was enabled so trust in Jesus as my Savior.

Read the New Testament impartially - and you will always find that those who were baptized were believers.

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For further reading: You may want to peruse our small section of excerpts on Baptism.