Personally, If a fullsize (Tundra, Titan, F150, RAM, Silverado...take your pick...) will fit where you need it to, I'd go that route. With two growing kids I think you'll outgrow that truck.
(Had an '03 Xterra Supercharged and loved it but, the Suburban we got after worked better for our needs)
But, that's just my opinion as a father of two that also travels with a dog. If you've driven the Frontier with everyone on board and it works for you, have at it.
Just out of curiosity, what are you driving now and how do you find it during road trips?