Where are you? There are some places I can recommend, primarily North Jersey, in winter:
Children's Museum of NJ, Paramus ($10/person to climb on real fire truck, play in sandbox, shop in pretend grocery store etc.)
In the Swing, Waldwick ($5 to access "playland" climbing gym, call ahead to make sure they are not booked for a birthday party)
Garden State Plaza Mall, Paramus - "playtown" free small indoor foam structure play area, plus $2 carousel and some small car rides
Imagine That, Florham Park - children's museum with a great arts & crafts area
Liberty Science Center, Jersey City - children's play area downstairs with some water play, balls, cars, climbing equipment
Funtime Junction, Fairfield NJ - haven't actually been to this one, recommended by friend - another climbing gym open play space you can pay to go in when they don't have a birthday party going on
Any Barnes & Noble - weekly free storytimes (see website) plus Thomas train table in children's area
Ride the train - go to your closest stop, ride to the next stop, cross platform, get back on and go home - toddler heaven for about $3.
Children's Museum of NJ, Paramus ($10/person to climb on real fire truck, play in sandbox, shop in pretend grocery store etc.)
In the Swing, Waldwick ($5 to access "playland" climbing gym, call ahead to make sure they are not booked for a birthday party)
Garden State Plaza Mall, Paramus - "playtown" free small indoor foam structure play area, plus $2 carousel and some small car rides
Imagine That, Florham Park - children's museum with a great arts & crafts area
Liberty Science Center, Jersey City - children's play area downstairs with some water play, balls, cars, climbing equipment
Funtime Junction, Fairfield NJ - haven't actually been to this one, recommended by friend - another climbing gym open play space you can pay to go in when they don't have a birthday party going on
Any Barnes & Noble - weekly free storytimes (see website) plus Thomas train table in children's area
Ride the train - go to your closest stop, ride to the next stop, cross platform, get back on and go home - toddler heaven for about $3.