4 week Family trip to London/Paris/switzerland..need help

Seems like a pretty well-thought-out itinerary.

You have many options for your return flight, so you could pick the one with the =flight that works best for your family.

First would be Lyon St.-Exuperey, with your proposed itinerary. Or deGaulle, with a 2-hour direct train from Lyon.

If you tweak your route to go Alsace > Lyon > Switzerland (as opposed to Alsace > Switzerland > Lyon) you have the choice of Zurich, Basel, and Geneva airports. Geneva is also an option from Lyon. All by train, so plan an afternoon flight.

St Exuperey is logistically best from the point of view of ground logistics, the question might be whether it works as a departure for you.

Hello Lisa. That is a good itinerary. You said your last destination will be "Lyon 4 nights ...or another place ..." In France, I would prefer to go to Dijon, rather than Lyon. The travel route that I would choose :
When I depart from Strasbourg or Colmar,
ride in a railroad train to Dijon.
When I depart from Dijon, ride in railroad trains to Switzerland (probably ->Bern ->Interlaken ...).
Fly from either Geneva or Zurich airport toward your home. The night before the flight from one of those airports, I would be at a hotel that is located very near the airport. Big hotels are located very near the Zurich airport, with a shuttle bus for your transport from the hotel to the airport. If you choose to fly from the airport of Geneva, you could be at a hotel at Lausanne (at the north side of Lake Geneva) the night before the flight.