Not to be a downer, but if you're asking these questions, should you really be taking toddlers out there at relatively high water for their first trip? How well do you know that section of river? Have you scouted the takeout and dam?
Sure, folks will say "it's just the Platte" but at higher water, any river will be swift, there may be (urban) hazards, and you may be in for more adventure than you want with kids in the boat.
Be prudent, be safe,
Nothing in the world is more yielding and gentle than water. Yet it has no equal for conquering the resistant and tough. The flexible can overcome the unbending; the soft can overcome the hard. - Lao Tse