You could do all that with easy train connections. Zurich via Basel to Colmar is a really easy operation.
If you stick with the plan to drive you will need to obey both French and Swiss driving laws, especially around the transportation of your 8 month old and your 3 year old. The law for France is by kg weight and age, in Switzerland it is by cm height and age.
A guide to the French law:
everyone in a car has to wear a seatbelt at all times. If you have children with you then make sure you obey these rules on car seats and restraints:
All children up to the age of 10 must travel in a car seat or restraint. The use of car seats is determined by weight:
Under 10kg: Rear-facing seat in the front passenger seat (with passenger airbag deactivated) or back seats.
10 - 13kg: The same conditions as above apply.
9 – 18kg: Child seat with included harness or protection tray.
15 – 25kg: Booster seat used in conjunction with adult seatbelt.
22 – 36kg: The same as above.
Children under the age of 10 cannot travel in the front seats without using a child restraint. The only exceptions are if there are no rear seats, the rear seats are already occupied by children under 10 or if there are no seat belts.
and of Swiss law:
Child seat or seat belt? Children under 12 years must sit in a special
child seat if they are under 150 cm tall. Children over 150 cm tall
and children over 12 years of age must wear a seat belt.
Acceptable child seats Children must be secured in the correct child
seat for their weight and age. The seat must bear the correct ECE
security label.
Children in the front seat In principle children are allowed to sit on
the front passenger seat regardless of their age. If your car is
equipped with airbags, rear-facing car seats may only be used if the
front airbag on the passenger’s side is deactivated.
For detailed information on how to secure your child in the car go to
the Federal Roads Office website.
Fines The fine for transporting an unsecured child under the age of 12
is CHF 60.