The InSim plastic surgery component requires Uni. I know, because I didn't have Uni for a long time after I started doing this story (my only other EP was NightLife), and that was why all of Cenwulf's babies with Colburga had to die!

I don't think there is any other way to modify Sims' facial features. Tweaking the mesh structure of the face is pretty complicated work (you would basically need a mesh-making program to do it) so I don't know who would write one when you could just buy Uni. (Unless you wanted to do some really crazy tweaking... something the in-game facial sliders don't provide.)

Anyway, I've never heard of such a thing.

If you're really set on keeping your kids' features mostly intact, but just tweaking a few things -- and if you don't mind adding some extra Sims to your game -- here is what I would recommend. This is how I make CAS-children for Sims who already exist in-game.*

1. Start SimPE, load the neighborhood, open SimSurgery, and select the Sim.
2. Click on Export beneath his picture (I think that's what it's called... going from memory here...) and save the Sim. Normally the saving location should be in your "EA Games/Saved Sims" folder.
3. Start the game and go to CAS. Pick the appropriate gender and age, and then go to the pre-made Sim bin. Find your exported Sim and select him.
4. Tweak the face. Save the family. (If the Sim's a youngster you'll have to save him as an adult, but you can age him back to a child with InSim.)
5. Go to the lot with the real Sim. Teleport the cloned Sim in, add him to the family, tweak any family tree settings ("set as my parent", etc.).
6. Kill the original Sim or move him out and make him an "extra" or something.
7. Optionally go back into SimPE and fix his genes so he has his correct DNA inherited from his parents rather than the CAS defaults.

Or, after step 4, instead do this:
5. Exit the game, load SimPE, and use plastic surgery with the new Sim as the archetype. That way all the original Sim's relationships, etc., will not be lost. But I have never tried this with Sims of different ages, so unless you made an extra placeholder adult Sim in CAS so that you could keep your clone Sim as the correct age, I don't know what would happen if you try to put an adult's features onto a child's.

Obviously this is kind of "expensive" insofar as you're creating another Sim. If I had known more about SimPE and exporting-reimporting Sims way back when Colburga's kids were dying off, I might have saved one or two in this fashion. To me it's worth it -- I do some crazy things with placeholder Sims and things like that, since for me telling the story is worth a few extra Sims hanging out in my neighborhood. But you (and your computer) might not feel the same way.

* When I'm making CAS babies "after the fact" in this way, I never actually save the cloned parent -- just the kids. For example to make Imin's family, I cloned Imin, created his clone in CAS, then created a wife for him, then made the babies, and then deleted the Imin clone before saving the family. Just thought I would make that clear.

I used to delete Sims pretty often (again, back before I could plastic-surgery them into another character) and never had a problem, but it's probably not the safest thing in the world. The place where I could see you running into problems is if you put the family on a lot, and they meet the neighbors, and so on, and then the neighbors will have relationships and memories for Sims who are now deleted.

If you tried the 2nd method I listed, you're probably safe though, since they never left the family bin and never got any relationships or possessions or anything.

But I really hesitate to say "Yeah! Go ahead and do it!" because I would hate to be responsible for breaking someone's game. It's some kind of miracle that I've never destroyed Lothere, with all the crazy stuff I do in SimPE. *knocks on wood*