Young kids are not great at playing by themselves. Pretty much the only way to get a preschooler who can't read yet out of your hair for an extended period of time is to give them an iPad or TV.
This is better with more open space. A toddler I know can occupy himself for hours outside, but you have to keep a watchful eye for what he's getting into, so it's not as relaxing for a caregiver as a tablet or phone.