1. When bathing the baby let the older one soap the baby's feet and or legs.
2. If they want to carry their sibling, sit on the couch beside each other and lay the baby's legs on top of her older sibling.
3. The older sibling can also wave a few toys in front of the baby.
4. If you pat the baby to sleep, the older sibling can help you pat the baby's butt.
5. For the older ones who can control their movements mo, they can help mix the formula for the baby, just make sure the water isn't too hot.
I saw M1 becomse giddy with joy the 1st time her sister squeezed her finger and help onto it tight. M1 exclaimed "Shobe hold Maxine's finger!". She loves it too that her sister watches her and her sisters loves watching her because she's so on the go all the time.
You can just think of the small ways the older sibling can be involved, the older they are the more they can contribute. But no matter the age, always be careful with both of them. It also helped that I let the 2 kids spend time with each other without their momma and poppa. So M1 got used to having her sister with her without her feeling the need to become crazy jealous. Everyone has their own personality and will take having a new child in their own ways. Its all up to the parents to help ease them from solo artist to becoming a duet.