The Museo de los Niños in Abasto is a fun and interactive children's museum in the Abasto Shopping Mall.
There are a variety of hands-on exhibits and activities designed to educate and entertain kids of all ages. It really feels like a kid sized version of Buenos Aires with a kid sized city bus (colectivo), a Santander bank, a COTO supermarket, a news station, a football field, and even a candy factory. (Yes, there is some brand marketing being done but the kids love it, what can we do?).
There are three time slots to visit and you can reserve in advance to avoid a line but it's not really necessary otherwise. There are a LOT of available slots and I've never seen it sold out. You'll pay for each child (but 2 and under is free) and adult but the adult price is minimal.
At the time of writing, for example, a child's entrance fee is $9,000 pesos and an adult is $2,000.
You can bring your stroller in with you but you must keep it with you at all times. I've never had any issues pushing ours around with us.
All ages, really? And yes, while this museum is for "all ages" I mostly recommend it for older toddlers and up. There is a soft play area for babies that is great if you have a little sibling you have to entertain, but it's not exciting enough to be worth the visit on its own (in my opinion). For a soft play space that will really rock their world, go instead to MIJU downtown.