The points below illustrate how Kiddle returns results for each query (in the order shown):

• Safe sites and pages written specifically for kids. Handpicked and checked by Kiddle editors. 
  Typically, results 1–3.
• Safe, trusted sites that are not written specifically for kids, but have content written in a simple way, easy for kids to understand. Handpicked and checked by Kiddle editors.
  Typically, results 4–7.
• Safe, famous sites that are written for adults, providing expert content, but are harder for kids to understand. Filtered by Google safe search.
  Typically, results 8 onwards.

Since Kiddle results are either handpicked and checked by their editors or filtered by Google safe search, you can be confident you'll get kid-oriented results without any explicit content. Plus, when some bad words are present in a search query, their guard robot will block the search. 

The BBC reports that:

Kiddle was registered in 2014 and is powered by Google safe search but has no connection with the tech giant.

They also explain that Kiddle is causing some controversy by blocking many common search terms. Read the full article here.