trip to Denver, tips?

Denver isn't in the mountains. It is on the plains. There are some nice city parks with playgrounds, a great aquarium, a zoo, a natural history museum, and a children's museum. If you want the mountains, you need to go to the mountains. You can get to Genesee and Evergreen is about 30 minutes from downtown Denver. There are parks and trails and all that and it is the mountains. If you want to go further, going west on I-70 will take you to a lot of great places.

Don't bother with Estes Park. (Sorry, EP folks). It is very touristy. and much farther north. You don't want to waste a lot of time in the car with a baby.

Something really important to keep in mind: March is historically the snowiest month in Colorado. It could be 70 degrees and sunny or there could be 2 feet of snow.

I'd second the suggestion for Estes Park, more precisely go to Rocky Mountain National Park. You need to go about 45 min north of Denver on I25, then west on Colorado 34 (Loveland exit). RMNP entrance is near Estes Park. End of March there will still be significant snow on the ground in the park and Trail Ridge road will likely be closed at some point. Estes Park is small touristy town. Maybe stay at the Stanley Hotel?

Denver is just a city, nothing special to see there.

Denver is a real nice city but it's till a city. Google Denver tourism, I haven't been there in a fair time. You will be there for spring in the Rockies. It will be well worth the investment to take a drive west. Boulder is also nice, Vail isn't that far, and there's Breckinridge and many other places. It will be gorgeous that time of year.

well...Denver is a major city. It would make sense to have to drive an hour...but Estes Park is nice.