[constantwanderer]

Your mother-in-law's opinion is one of the silliest things I've ever heard about a child's activity level. Just because young children tend to be active in short bursts (is has to do with the different energy systems in their body having different capacities than an adults) that doesn't mean they are not capable of being active for extended periods of time. And I cannot think of any way that your child's joint health will be adversely affected by walking for 30 minutes. I suspect any colleagues out there specialized in paediatric orthopaedics will agree with me in this matter.