Meet the Wonderfold W4 Elite Stroller Wagon: a collapsible, folding wagon with room for up to 4 tiny passengers. It has a removable/reclining seats and 5-point adjustable safety harnesses. This wagon is designed for kids 6+ months old and has 99 weight capacity per bench (total of 300lbs).
You can always remove seats when your kids have grown to turn this into a beach wagon. The W4 Elite has a slidable, removable canopy, easy-access front zipper door, and a loads of storage on the sides. The push handle is also adjustable.