Formal:
* Bienvenue à la maison, mes chers enfants. (This is a very formal and respectful way to say it, emphasizing the "cher" for beloved.)
Informal:
* Bienvenue à la maison, mes petits/mes beaux/mes belles enfants. (This is a more casual and affectionate way to say it, using "petits" for little ones, "beaux" for boys, or "belles" for girls.)
* Rentrés à la maison, mes chouchous ? (This is a very affectionate way to say it, using "chouchous" as a term of endearment for darlings or favorites.)
Other Options:
* C'est bon d'être de retour à la maison, mes amours? (This translates to "It's good to be back home, my loves?")
Ultimately, the best way to say it depends on your relationship with your children and the tone you want to convey.