Breastfeeding toddler and newborn

So my newborn is a month old and my toddler is 3, my toddler was bottle fed where as my newborn is breastfed. Recently my toddler has been Ill he’s got a cold, sickness, fever so I’m hoping it’s not rsv. I was wondering would I be able to give my 3 year old breast milk in a cup as my newborn has it off the boob or pumped. Would it have the same benefits for my toddler as it does for my new baby?

Many thanks