Not sure this is the right place for this - hope so!
With ds1 I really can't remember what we used! Cushions and maybe his carrycot but nothing specific. Now with ds2 hitting 6mo I've had much less time to work with him on sitting and so on, and I can't see that changing with a toddler in tow.
So what one product could I best use at home for him to be trapped in sit in and play?