Regular shoes are good, The Young Bloke loves to climb over rocks and logs, run about etc when we stop for a rest. When off-road he needs sneaker grip to help push the tandem up steep un-ride-able sections.
He learned to manage the toeclips and straps very quickly at age 3. Off-road these days we both use flat pedals no straps. On-road he still has clips and straps.
Half your luck, I would love to do a 7 day event with my boy. What fun!