Congratulation and best wishes for many happy years with your family.   More than 35 years ago as the new mother of twins and an 18 month old I needed to find answers to this question.  If you remember this was before the days of infant car seats and the newer strollers/joggers.  My solution for the shopping trips (I mainly did grocery shopping in those days!)  at that time was to put kids in one cart, reclining, seated, or standing, and groceries in the second cart...