I am 10 years older than my first sibling. Yes the baby was neat for a while, but as I became a teen and mom had a few more kids, the neatness did wear off. I babysat them a lot and became almost like another parent to them. We are all adults now and age doesn't matter.
I would suggest making as many family traditions as possible that would involve your kids doing things together. Gardening, carving pumpkins, vacations (or a day at the beach) is all it takes. Removing outside distractions so that the event is just your family will keep the kids close.
hope this helps