Hey Caroline.
I love suggesting good contemporary Christian songs and music videos. They're a neat "bridge" between faith and popular media for this generation (and me too). I'm sure there are a couple of "kid songs" out there about baptism, but I tend to shy away from "cute kid songs" 
I listen to a lot of Christian music on YouTube. All the best songs are there (and all the awful too). The visuals are often striking. Sometimes you have to search for a song you like to see it with the visuals you'll like. There are several "baptism" music-video-songs out there. Most I do not care for. Not many that are very catchy. And some that simply aren't very contemporary or kid friendly. Carrie Underwood has one, but her "official" video of it is ridiculously secular. Go figure.
Here are a couple I do like:
(1) "Come As You Are"
Crowder the artist has an interesting appearance! but is a good singer with a great song titled, "Come As You Are." Here are two youtubes of it: his official video and a more interesting fan video with good images. "Come As You Are" is an invitation to believe and be baptized.
When I see and hear the phrase "lay down your burdens" in his song lyrics, I can see a person laying back in the water being baptized. The word "shame" is an antonym of the baptismal words "clean" and "wash." We "come as we are" to baptism, warts and all. The only prerequisite is a desire to seek and know Jesus.
Excerpt:
So lay down your burdens
Lay down your shame
All who are broken
Lift up your face
Oh wanderer come home
You're not too far
So lay down your hurt
Lay down your heart
Come as you are
(2) For This Child - (the Baby Dedication Song) by Ken Blount.
When I first heard it, I imagined Mary dedicating Jesus in the Temple on the 8th Day. Preview it at https://youtu.be/Qyb8NmtSxTk The artist sells the unbranded full video for $5 here. It's sweet, almost like something you'd project in worship.
(3) Who I am by Casting Crowns
I'm adding this one. Though it's not really about baptism, it does speak to the "acceptance" which baptism primarily signifies. It's lyrics are very visual, so could be acted out. This is one of their currently popular songs getting a lot of radio time.Great tune and teaching whether for baptism or not.
Who am I, that the lord of all the earth
Would care to know my name
Would care to feel my hurt?
Who am I, that the bright and morning star
Would choose to light the way
For my ever wandering heart?
MISC: Came across this instrumental song that features a LOT of video of John and Jesus in the Jordan. The video is cribbed from the (free) Life of Jesus Christ movie available online.
Let us know what you chose and how you did it!
