Pics of those things seem to get posted every year. I don't think they've ever been 100%
firmly ID-ed.
A couple of suggestions have been slow-release fertilizer that was part of the soil mix -- that's my personal favorite, BTW -- to bits of perlite or vermiculite congested with water. I seriously don't think they are bug eggs of any kind, though.
It's quite possible that you just didn't notice them in the soil mix. Pellets of slow-release fertilizer, such as Osmocote, are smaller and opaque, but after they've been in the soil for awhile, they absorb water and become more obvious.
If you want to run a test, you could put a bit of the soil with the "eggs" in a jar with a lid, put holes in the lid, and keep the soil slightly moist. If these are eggs of any kind, they should hatch, and you can see what the critter is. Might be a fun project for a child who has an interest in bugs. It would be nice if you posted pics of the project, so we could finally confirm or deny that they are insect eggs.
