Is it appropriate to say "Mwen lanmou ou." to your children or is that phrase used only in a romantic sense?

The word 'lanmou' which means 'love' is a noun in Creole.
So you will use 'renmen' which is the verb ' to love' in English.
And no, it is not only used in the 'romantic' sense.

Mwen renmen ou.
I love you. 
Haitian Creole ↔ English Reference (a work in progress at this time)