how many kids? I recently took a pic for a friend who's one of 16 siblings...
As to the question... no idea what an Olympus OMPC is (I've seen OM1/2/3/4 & 10s) but it obviously takes Zuiko lenses which is a good thing. The 1st two lenses mentioned with the Yashica would be ok I'd think, the 3rd might be a bit dodgy (quality wise) You'll be able to buy used lenses for both for reasonable amounts (or lots.. I think you can put some Contax lenses on the Yashica) The Yashica offers more mm but the Oly has wider (more suitable at times) but either case is easily fixed with another cheap lens
Things to contemplate...
- Age/Condition of the Yashica (might not be very old at all)
- How each camera feels in your hands. Do they feel comfortable.
- Warranty of the repair vs Warranty of the Yashica?
- Auto mode available with Oly.. is that needed?
In conclusion.. I dunno! If the Yashica looks like it's had little use, I might be swinging towards that.