We did not make them share food gifts they were given, but we did not let them eat those gifts in front of others who didn’t have a treat.
Community property toys: even if a toy is community property, the child who is currently playing with it is the one who has priority. I have shared property in common with my husband, too, but it’s incredibly rude and selfish of either of us to come up and demand that the other give up something that is *currently* in use just because we want it.
“Because he’s a baby”- as a firstborn, I never loved this rule. I wouldn’t make a two year old give what he is playing with to a 15 month old. We would have either distracted the 15 month old ourselves, or we would have worked on teaching the 2 year old how to distract a baby by giving the little one a different toy. He wouldn’t have to try endlessly, either- just pick another interesting toy out and try to give it to the baby. If the baby is still demanding big brother’s toy, mom would intervene.
We use sign language from birth at our house (because we have a disabled child who cannot speak), so this also works for us: when a baby screamed at an older sibling for not giving up his toy (or any reason that wasn’t essentially self defense, I’d remove the baby, saying, “you do not scream at your sister,” and have baby sign an apology (hand over hand if need be).
Non-community Property: I don’t think children need to be forced to share their private property. HOWEVER, if company is coming, I would have children remove any special toys they don’t want to have other kids play with. And if gloating and lording it over the siblings and trying to coax them into covetousness or discontent, then we dealt with that issue. In such cases the issue isn’t sharing or not sharing, it’s gloating.