if you are making both crib and changing table, the options are near limitless.
personally I would go with bolting them together. nuts&bolts have a tendency to be quite strong and not loosen up . . . (g)
for the threaded part you could use
a T-nut "embeded" in a post/stile,
a thread insert
or a completely thru bolt
some washers required . . .
thru bolting with a Nylock nut would be very secure.
bolt heads/nuts can be recessed . .
or just a length of aluminum angle bolted/screwed to both pcs.
I would suggest attaching it at the top and mid-to-bottom somewhere - otherwise if only the top is attahced should someone move / lift one of the pcs they might have considerable leverage to rip out the attachment points.
the countertop bolts are not the best option imho.
if you use a thread insert in hardwood, don't believe the printed recommendation of drill hole size. do a test install in your wood species. a thread insert in pine is a different animal than a thread insert in hard maple....