A mom after my own heart! (Okay you may be a Dad, can't really tell!

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We are a family of five and just took our first ever cruise. I think we probably booked pp cheaper than anyone...we invited our parents along so we got 7 for $630 pp for a 10 night cruise in the Mediterranean (granted that was only the cruising part and airfare was not as nice as it had been in the past but you're asking cruise questions)
We got this b/c like another diser stated you can take advantage of kids sail free offers...so per paying adult you get one child free...so in your case you'd need to pay for 2 adults and one child (do the younger one and let the older ones go free..)
The best times to go are January, May and September (rate wise) it's all about supply and demand...many families can not travel these months due to school limitations..other months have exceptions because schools have fall breaks in October/November Christmas breaks in December and spring breaks starting in Feb-April....January is just not usually a good time to sail b/c of iffy weather...so shoot for May/September if you can.
Book 2 inside 12 category rooms...the only problem with your situation is you would need to put one adult in each room,
my suggestion would be to put 4 of you in one room and one in the other because cat 12's only fit 3...if you put 2 & 3 then you might end up with cat 12's...but many times they will upgrade you especially if you have 4 in the room...and they try to keep you all together so the opportunity for a free upgrade might be better doing it the way I mentioned...we had 4 in one and 3 in the other and they moved us to a category 9 (big window, outside stateroom) adjoining room...it was wonderful.
Now if the economy still suffers..they are going to have a hard time filling slots on the Magic and the Wonder...most loyal Dis cruisers have already booked their Dream and the Fantasy is supposed to roll out the next year (2012?) So Magic and Wonder will most likely offer some very attractive deals...I thought we would really like the veranda and considered upgrading to a cat 4...but it would have cost us $1800 more at port and to be honest, having the two rooms gave us much more space not to mention two bathrooms and extra closet storage..
Hope this helps!!
Tara