These aren’t exactly exploration games, but they’re simple games that my toddler likes too:

• Animal Crossing is easily her favorite. She loves “helping” my wife pick outfits and fish.
• A Building Full of Cats is short, cheap, and cute. She likes making up stories about each apartment and cat. There’s also tons of similar games in different locations.
• Cats in Time has simple puzzles that she can do with a bit of help.
• Slime Rancher might be a good fit. It’s simple and cute with a focus on exploration.
• Dorf Romantik is a relaxing and cute game that’s a good introduction to resource management. She might not be good at the actual goal of the game, but she likes placing tiles.
• Subnautica in creative mode might be interesting for exploration, depending on how sensitive your kid is about some of the darker areas and creatures.