In baptism, water is poured or sprinkled over a person in the Triune name. Why does baptism use water? To grasp the full meaning of baptism, we need to grasp the meaning of water in the Scripture. Water was chosen for a reason, having to do with both its symbolism and its practical uses. Water is a fitting instrument for God’s purpose.

Water has been part of the creation from the beginning, when water covered the earth. One of the church fathers said, "God is never without his water.” And this is true — when God shows up again and agin, he has his water with him. God has been working with and through water from the beginning.
Water is foundational to human life and culture. Water is necessary for life and civilization. 
Water makes things grow. Water brings fruitfulness.
This is why cities would often be built near rivers or lakes or other bodies of water. Water brings life, water sustains life. In Genesis 2, water combined with human labor to make the land productive. This is still true today — water plus labor equals civilization.
Further, water often forms boundaries. God formed a watery boundary between heaven and earth on day 2 of the creation week. National borders and state lines are often watery. Or think of a moat around a castle, forming a boundary to protect it. This is why so often in Scripture a sea crossing or river crossing is treated as moving from one domain to another. To cross over water is to cross into a new realm. Water can serve as doorway or passageway. 
Baptism is all of these things. Baptism is a water crossing. Sea crossing and river crossings are treated as baptismal events in Scripture. They are transitional. The baptized one moves from slavery in Egypt to the joy and freedom of the promised land. He moves from the domain of darkness to the kingdom of light. This is why we have our baptismal font at the door of the sanctuary — in baptism one passes from the world into the church. In baptism, we pass through the heavenly ocean into the heavenly sanctuary. Baptism is a border crossing. Baptism brings us to a new place. 
And further, baptism is about growth and fruitfulness. God waters us with the Holy Spirit to make us fruitful, to grow us, so we can become a part of producing the godly culture and civilization that is the basic human task, going back to Genesis 1.
These children come to be baptized today that they might enter the kingdom and bear fruit. They are different ages but they will receive the same baptism — with the same gifts and promises, the same privileges and obligations.