My DS is nearly 3 and is our only child. I went to a soft play with some friends today and I couldn't help but notice how confident their two boys were straight off into the climbing frames and down the slides and got stuck right in. They are both second children and have older siblings to encourage them and follow.
I noticed the difference how my only child was more cautious about entering the soft play and analysing the routes and slides etc.
Have you noticed this with your only child or child with older siblings?