Paris to Disneyland and back

Hi there,
This one's a bit tricky because of your arrival day in between Navigo week pass validity, so I understand the difficulty in finding a solution.  I'll give details then summarize what to buy at the end.
For day one, I would go with a Navigo Easy card with a Navigo Day Pass 1-5 zone on it (for each of you, unfortunately no discount for the kiddo.) This covers your CDG to Paris, trips in Paris, and Paris to Disneyland (Marne la Vallee) trip.
For the 2nd part where you travel from Disneyland back to Paris, spend 2-days in Paris, then back to CDG, this is a bit more complicated.  For Disney to Paris, a single-use paper RER ticket (cannot be put onto your Navigo Easy card).  It'll be 5euro for each of you.  For the 2 days in Paris, I would go with a booklet of 10 Ticket t+ on each of your Navigo Easy cards.  This would likely give you enough coverage for the 2 days about Paris.  Then finally for the Paris to CDG trip a single-use RER ticket.
 
Summary of what to buy at CDG airport train station ticket office, from the helpful/friendly/English speaking agents:

• Navigo Easy card x2
• Navigo Day pass 1-5 zone on each card, for use immediately
• booklet of 10 Ticket t+ on each card
• RER ticket (paper) for Disneyland to Paris x2
• RER ticket (paper) for Paris to CDG x2

The Navigo Day pass and the booklets of 10 tickets can live on the Navigo Easy card simultaneously.  The Day pass will be used first before any of the 10 Ticket t+.  The RER tickets need to be paper because Navigo Easy can't hold RER tickets.
 
Let me know if you have any other questions.  Hope you guys have a great trip.