If you really want planned activities/hobbies that will grow with your child, I recommend the YMCA. We just joined ours and it is amazing and inexpensive for a family membership. For the toddler set, there is swimming/splash park (with lessons if desired), classes like tumbling, music, and dance. Then, there's also an outdoor trail system for all ages, a family game room for all ages, and drop in child care for when you want your child to play while you work out. As the child gets older there are more classes and sports teams available, plus different clubs (like a teen club or a board game club). They'll also get access to adult classes and gym areas, like the climbing wall and frisbee course, as they get older. The Y also has a full calendar of family activities that inlcude toddlers -- movie nights, craft days, plays, etc.
I wish we had known about the Y when my boys were younger.