"Fun-filled" is almost always followed by a noun, so it is written with a hyphen.

How do you use fun-filled in a sentence?

After a fun-filled day, a nap in the cabin is always a delightfully restful option. The sexy singer said she wanted to make sure her children grow up in a fun-filled environment.

Is fun-filled a real word?

Fun-filled is a lovely compound adjective used to describe something that is great fun pretty much all the time, or that everything about it is fun, and it refers most commonly to an experience or an object, rather than a person.