I love flying SW with kids. it's the best family airline for domestic travel imo. I'm not springing for my herd of children to sit in the front of the bus so I may as well fly SW.
I'm flying my entire jumbo family on Frontier in December. I haven't flown Frontier for like 2 years. I got the package deal where you get 6" more leg room and ability to select our seats, free cancellations and changes, free checked and carry on baggage, some other crap. it wasn't very expensive. 4 seats RT to Disneyworld was like $1,300. I will report back on how travelling with shitloads of kids compares between Frontier and SW.
Also, Frontier is getting TSA pre in like August.