tobiano= white crosses over the shoulders, generally have the facial features of a solid colored horse..ie star, snip or strip and leg markings that are mostly white
Overo = white does not cross the back, have wild facial markings such as blaze and high leg markings,ie stockings
You can have a horse that combines the two patterns-thru genetics and this is called a Tovero....and it may exhibit combinations of both above horses....the most common as the horses typically shown in tv as "Indian" horses......mostly white with a chest "shield" of color flank color and a bonnet of color over the ears. Most times these horses will have 1 or both blue eyes.
On a side note my absolute FAVORITE pattern in paints is called a "splashed white". This particular horse is an overo pattern, but the horse looks like it was lifted and then dipped into white paint. Absolutely LOVE it on a bay horse....stunning!!
And to keep this on topic.....I would say your shrimp are overo.....altho they do exhibit tovero coloration in some with the white going over the shoulder..... ;-)