It’s ok to come from humanities background. Same to me but I self study a lot of anatomy during the program. Lots of free materials online.
if you know OT is a your passion do it asap as experience matters a lot. If you can handle an undergrad you can properly manage a master. Some schools make their master programs slightly harder but making it harder to pass or asking for more critical evaluation during assignments.
Not much paediatric stuff is covered but it depends on school and teacher, I was covered on sensory integration and hand writing. It’s very basic. The system in the U.K. is getting training on the job more than teaching you everything in the program.