Some promises you just can’t keep. Like the one made nine months ago: swearing off hard rock once junior came along.

But now he’s here, and you can’t seem to get off the “Crazy Train.”

Hey, no need: There’s room for two with CribRock’s baby-friendly rock tunes. Full Metal Diaper is a collection of instrumental versions (xylophones and flutes) of favorites like Metallica’s “Enter Sandman,” Twisted Sister’s “We’re Not Gonna Take It,” and Guns N’ Roses’s “Sweet Child o’ Mine.”

If you vowed to stop living in the ’80s by the time your little angel turns 1, don’t worry. St. Elmo’s Pacifier has me-decade hits: “Hungry Like the Wolf,” “Girls Just Want to Have Fun,” “Take On Me.”

The tunes can’t replace the originals, but they’ll make child rearing a little more fun.

And help you keep your vow to rock your baby.

Available online at cribrock.com.