Hi Sally,
All of the major train stations in Paris have luggage/baggage storage service, including
Gare du Nord, the first station in central Paris along the
RER B train line from CDG to Paris.
Within
Gare du Nord the baggage storage room is located at the far western end of the station, down one level of stairs, to the right, through an enclosed/grill-gated area where you pass through baggage screening. In French the word for baggage storage is "Consignes". The first picture in the above link for Gare du Nord is looking west (towards the Eurostar end of the station).
From
Gare du Nord to Disney see my article on how to take a
train from Paris to Euro Disney. In your case, from Gare du Nord, take the RER D to Gare de Lyon (direction Corbeil-Essonnes) and then catch the RER A out to Marne La Vallée, which is the Disney station. You can't mistake this stop, as it's the last on the line. It takes about 35-40 minutes to go from central Paris to Marne La Vallée.
As an aside, you might be able to simply leave your bags with the front desk at the hotel if you arrive early. Then you can spend your day at Disney and check in that evening. Traveling from
CDG Airport to Disney by TGV train is much quicker than the city train, taking about 10 minutes.
Best Regards,
Ben