When we first planned this hike we had planned to take the funicular up to Plan Francey and then walk back down toward Moleson-Sur-Gruyere.  Unfortunately, we didn't realize that the funicular had not yet opened for the season, so instead we hiked up to Plan-Francey and then back down again.
Fortunately, it was a beautiful day, with beautiful views.  The path was wide and not very steep so the children did a good job making their way uphill with a bit of encouragement every now and then.
There were several nice distractions along the way, such as a shallow stream to cross and throw rocks into,  fields of bright yellow dandelions to run through and snails and other creatures to admire:
 The hike says it should only take about 45 minutes to climb uphill and 30 minutes to descend.  It took us about an hour and a half to climb uphill and about 45 minutes to descend.
Lucas was in the baby carrier for about half of the hike and he walked the other half.
We try to make sure when hiking with children to not keep too much attention on the clock.  It is more enjoyable for everyone if they enjoy the journey.  So remember to make frequent stops.  If they want to explore a certain area, then let them.  And, if you don't make it to your destination, don't worry - just enjoy the journey!

NOTES: 

We parked at the funicular station.  The walk starts just next to the station.

Other Hikes in Moleson:

Le Moleson to Plan Francey Via The Tremetta Trail

A Funicular, A Cable Car and Hiking in Moleson