From co- + sleep.
cosleep (third-person singular simple present cosleeps, present participle cosleeping, simple past and past participle coslept)
- (intransitive, chiefly sociology) To sleep in the same bed (with someone), especially of a family member, parent, child etc. [from 20th c.]
2005, Lauwers & Swisher, Counceling the Nursing Mother, page 259:
Both parents should feel comfortable with the decision to cosleep with their baby and be committed to following appropriate safety precautions.