All of the other posters have given good advice - you will see very little considering your actual full days are only Saturday, Sunday and Monday with a planned Friday to Tuesday trip. Travel days wipe everyone out - that's just a given.
The suggestion to use a long weekend holiday is really your best option - but that will require your husband booking the rest of that week off - in other words, he needs to be prepared to miss 4 weekday workdays (assuming his job is Monday to Friday - if he works weekends at all, you would have to adjust for that).
The next couple of holiday weekends where the parks will be slower are Labour Day and Canadian Thanksgiving. This has the benefit of lower crowds and lowest costs - it's value season at WDW during those times. The Labour Day weekend has the added advantage of the current Free Dining promotion - but the added drawback of intense Florida heat and the fact that it is hurricane season. A hurricane isn't really a problem for WDW itself since it is far enough inland that only a really big one heading right for the state becomes problematic, but a hurricane in the area could possibly disrupt flights for a day. Candadain Thanksgiving avoids the heat and hurricanes for the most part, but the discounts for that time won't be quite as good as Free Dining - there should be some discounts available though.
If you can go over one of those holiday weekends, Labour Day itself will be busier at WDW than the Canadian Thanksgiving Monday - so that is another factor to consider.
To maximize your time, you would want to leave on the Saturday before the holiday weekend and return the following Sunday - this gives you 7 full days at WDW. However, airfare on Saturday will be more expensive - the Sunday flight should be a little cheaper.
Next, Sundays at WDW are one of the busiest days in the parks - especially the Magic Kingdom - that would be your first full day there, so you might want to start with a different park even if the kids are itching to get to the MK.
Even with 7 full days, I would suggest (considering the age of the kids) no more than 5 park days - or perhaps 6 park days if one of them is at one of the water parks where they can play in the kiddie areas. Otherwise, take two full days off to recuperate. This is especially vital if you went during the Labour Day period - the heat will wipe all of you out. Trust me on this.
I would also suggest staying ON SITE! Get an early start to your day and try to get to the parks at opening time - especially during the Labour Day week. This will avoid the crowds and the worst of the heat in the afternoon. Do the parks until around lunch time - perhaps grab food in an air-conditioned restaurant before leaving to go back to your onsite resort for an afternoon rest - YOU'LL NEED IT!!! IF - and I mean IF - you feel rested enough after that, you can go back to the parks around dinner time (lines will ease off again - and so will the heat) and stay for a couple of hours before heading back for the kids' bedtimes.
On your (at least one) break day, do nothing other than enjoy your resort - swim in the pool(s) - the kids will be happy with this in and of itself - and perhaps pick a break day to take in a character dining experience at one of the resorts. Make it a VERY relaxed day - you'll be glad you did.
Finally, remember that the 5 year old - depending on their height - will be able to go on a lot of rides that the 7 month old cannot - even something like Goofy's Barnstormer as a very minor roller-coaster is out for the youngest. This means that as parents, you will be sacrificing what you might want to see to ensure that the children are having fun - and if both of you want to ride something the 5 year old can ride, but not the 7 month old - it will take extra time because you will need to ride twice (read up on the "baby-swap" in any Disney guide to find out how to do that in the shortest amount of time possible).
Anyway, 5 days in the parks is really about the minimum to do Disney well for a first trip - this gives you the chance to go at least once to each of the 4 main parks, and likely a second trip to the Magic Kingdom, since this is likely the one your 5 year old will want to see twice - although that's just a guess based on my own kids, who where 6 and 2 on their first trip.
With seven full days, I would suggest two park days, an off day, two more park days, your second off day, and a final park day before leaving. You'll get to see quite a lot - but obviously not everything - that's why you'll go back again someday! You also won't burn yourselves out - if you try to see all four parks in only three or four full days, you'll need a vacation AFTER getting back home.
Good luck, and I hope you have a great time!
),then a shorter stay might be OK.
) turned into a 3rd in 2 yrs. We did 5 days first time but had 3 full days and 2 half days. We really only scratched the surface but did get to see alot of things that the kids wanted to do. We missed out on alot of the shows etc but did that 2nd trip. You may need to decide on 1 park to skip.
