Passing the baby directly from hand to hand is prohibited (until the baby attains independent mobility), whether or not you have older children present. When you, BeSha'ah Tovah, have another baby, you can put him or her down on a bouncer, an infant seat, on the couch (with you holding on till a moment before your husband does), etc. Your oldest child might also be able to hold the baby as an intermediary. With cooperation, creativity, and practice you will maximize the amount of time that you can fully comply with this halachah with minimum toll on the mother's mental health. Of course, common sense must prevail. It would be a distortion of halachah to endanger the baby in any way. Where there is no safe alternative, the baby may be passed directly, with great care taken not to touch.
When a child reaches an age at which he or she can propel him or herself, there is room to allow passing directly when the infant reaches out and motions toward the other parent. Infants can also be manipulated to reach out to a spouse.
We would also like to direct you to a longer answer we have drafted on the issues of handling the laws of niddah after childbirth.