I'm pretty sure it's Ricinus communis; its not entirely clear from the photo because of the way the light falls, but as you've got young children, I suggest you remove it. The seeds are highly toxic, but the biggest problem with this plant is its fine pollen when in flower, which can cause asthma attacks. Allergic responses to the leaves and stems are not uncommon either, so although its generally safe if you don't eat it, I wouldn't choose to grow it where there are young children. As you don't know whether it was deliberately planted or not, its probably wise to keep a check next year in case it's seeded itself and others pop up, though if you live somewhere with colder winters, that's much less likely. More info here https://en.m.wikipedia.org/wiki/Ricinus