Sandwell is great for smaller kids, the route is only 2 miles long and it’s easy enough to get around.
It can be busy of a weekend and especially bank holidays.
As mentioned there are plenty of other trails around and if you take a ride up over the motorway bridges to the other side there are quite a few activities and normally a burger van/ice cream van to have a bit of a break at on the benches by the tennis courts.
Just don’t leave a bike unattended for a second or it will go missing!
Edit… Trails have their own parking next to swan pool, as you come up the newton road from the motorway (M6, J7) take a left at the traffic lights and turn down Forge Lane. The car park will be on your right after about a mile.
At the sailing club here: https://goo.gl/maps/gW5Jo3sWtnP2