I want to create a safe outdoor play area for our babies (Tyla is almost 2 and Mazie is 19 weeks

) I would LOVE to hear your ideas for a contained outdoor play area. Do you have one for your babies? Even if it is a patio/apartment outdoor play area, please share. What works? What is safe and also fun? Our backyard is a little more than 1/4 of an acre and is not fenced. (Front yard faces a VERY busy street.)
Thanks for sharing friends!