I made DD1 plums when she was pretty young. Those were one of the very few homemade purees she would eat. I don't exactly remember how I made them, though.
BFP1: DD1 born April 2011 at 34w1d via unplanned c/s due to HELLP, DVT 1 week PP
BFP2: 3/18/12, blighted ovum, natural m/c @ 7w4d BFP3: DD2 born Feb 2013 at 38w4d via unplanned RCS due to uterine dehiscence
Re: plum vs prunes
No idea, but I gave my DS1 plums all the time as a baby - steam and puree away!
BFP1: DD1 born April 2011 at 34w1d via unplanned c/s due to HELLP, DVT 1 week PP
BFP3: DD2 born Feb 2013 at 38w4d via unplanned RCS due to uterine dehiscence