Sacramento and Infants/toddlers

A few ideas:
Sacramento Zoo is great for a shady place to walk around
Walk the American River Bike Trail, but stay to the side to avoid bicyclists
Folsom Lake
Folsom Zoo (smaller than Sacramento's but nicely done. Also has a small train ride)
Fountains Shopping Center in Roseville. Has fun water features to look at, a water play area for young kids and a small train ride.
Gibson Ranch Park in Antelope area. Huge county park with farm animals, a large pond for feeding ducks, play equipment, picnic areas

Roseville has tons of great parks--visit their parks& rec page. One of our favs is the Riley library. They have a children's play area inside and an awesome playground outside.
Also many pools have a mom and tot swim time.

Stroller Strides is great!

Get in a mommy playgroup.....try meetup.com. when I moved here I had no idea where all the fun stuff was in Sacramento...so I started the Rancho Cordova Cradles to Crayons Playgroup...you are more than welcome to join....but there are tons of great mommy groups out there and some that are near where you live....all you do is enter your zip code and choose between playgroups, stay at hom moms, moms, etc...and it will give you a list of groups...you don't have to join just one..you can join more than one and try them out to see which one fits you and your children.

The mommy groups have playdates at peoples home, parks, public places etc.