This means being creative with the time that you do have and one very easy way to do this is to plan weekend / overnight trips. Honestly we do it all the time. We have even gotten it down so that we could do a spur of the moment - wake up and go - on a Saturday morning (of course that was with one child, we haven't attempted it with two yet).
There are a few ways that you can plan this -
First of all...are you planning in advance (weeks, months, etc...) or are you planning last minute within a week or so? This will determine the best resources for planning your weekend.
If you are planning in advance -
Go to the websites of the various towns / cities that you would like to visit and take a look at their calendar. They will usually have a calendar of events right on their website that will clue you in to when would be the best time to travel there. If you are trying to stay within a budget, plan a trip when there are smaller / local events (craft fair, music on the town green / beach, kids festival) these are events in which you won't find a lot of people traveling from out of town to attend. The events can still be an enjoyable part of your weekend - but you won't have the added crowds or increased hotels costs that you may encounter if there is a Weekend Music Festival, a big name band playing a concert or other large events that may draw a crowd from out of town.
You will also want to plan / research what things you can do in that area that aren't too time consuming. On a weekend trip it is hard to do an amusement park because it will take a whole day. If you can find some things that will take a few hours (children's museums, parks, state parks, small fairs / festivals, etc...) you will be able to have a much more relaxed weekend.
In addition, when you are planning in advance be sure to spend some time looking up hotel prices and price shop the hotels. In doing this be sure to read hotel reviews to ensure that when finding a cheaper hotel you are getting all of the amenities that you are your family want / need. There are some great hotels that you can find for a relatively low price but again you want to find out as much as possible about these hotels to ensure that they are really the best value for your money. Sometimes we also take the opportunity of a one or two night vacation to spend a little bit more than normal on a hotel room. Since you are staying for a shorter period of time the cost doesn't add up as quickly and so you may want to take this oppostunity to spend a bit more for your room.
If you are planning a last minute trip
1.) Look for local last minute deals online. You can search any of the travel sites (expedia, travelocity, etc...) for last minute deals in your area. We usually stay within a couple hour drive from our house because you don't want to spend you whole weekend in the car.
2.) Use the Roomsaver guide / website (also see my "Roomsaver is my money saver " post). Pick one up and look through it for destinations that are close enough for a weekend and figure out where you will find the best deal. In the Roomsaver guide you will see that some hotels will say that you will need to add $20 for a weekend night - just be aware when you are looking at the prices to also take a look at the fine print. I will say that even adding the $20 to the price on weekends seems to get us a better deal than other sites or calling the hotel directly.
In these instances I suggest a place you have been to and are familiar with. When you are planning a last minute weekend away and aren't spending too much time researching hotels or what activities you can do in that area - it will benefit you greatly to go to a place that you are familiar with. You will know what hotels you like that are in your price range (and you can price shop those places through the ideas noted above) and you will have an idea of weekend friendly activities that you can do as well.
In any case make sure that you will have a relaxed, enjoyable weekend. It is never fun to try to cram so much into a weekend that you feel like you have had no time to relax, especially when you have to be back at work on Monday.
Also please take a look at my other Travel Tip Tuesday posts