My husband and I have already
taken several short trips (no more than 4 hours drive time each way) with our 1 month old daughter and they have gone great!
Even in cold climates (we live in Canada), I recommend finding a way to get outside with your kids every day (bundle them up and go
for several short trips outside if need be) and finding places for them to get exercise (playgroups and indoor playgrounds are great for this, but other options include going for a walk around a museum or a mall or other place where your child can walk for a long time).
When you are traveling on a budget, you may have
several short trips or a single large trip that account for the amount.