From my understanding from various souces stemcell works something like this.

Baby A stores stemcell sample A, Baby B stores stemcell sample B. If baby A has Leukemia, baby A can use the stem cell of baby B. Then the sample A has to be discarded as defective, since baby A is proven to develop leukemia.
So 2 stemcells can only be use by 1 individual, if you will only have 1 baby. Probably dont need to store any stemcell since using stem cell by themselves are not viable option as for now.