•Timing of immune organ development in minipig and rodent can be translated to human.•Knowledge on immune/lymphoid organ development is mainly based on the morphology.•Immune function development has been determined mainly in human, postnatally.•Combination of immune morphology and function is most informative.•Insight in immune development across species will facilitate clinical trials. A healthy immune status is mostly determined during early life stages and many immune-related diseases may find their origin in utero and the first years of life. Therefore, immune health optimization may be most effective during early life. This review is an inventory of immune organ maturation events in relation to developmental timeframes in minipig, rat, mouse and human. It is concluded that time windows of immune organ development in rodents can be translated to human, but minipig reflects the human timeframes better; however the lack of prenatal maternal-fetal immune interaction in minipig may cause less responsiveness to prenatal intervention. It is too early to conclude which immune parameters are most appropriate, because there are not enough comparative immune parameters. Filling these gaps will increase the predictability of results observed in experimental animals, and guide future intervention studies by assessing relevant parameters in the right corresponding developmental time frames.