How much is too much fluoride for a young child? Do I need to buy the "kid" version of toothpaste, or can my 4 year old just use regular toothpaste? Do I need to worry about my child getting too much fluoride? .

Where do you live. Check if you have fluoridated water where you live and if it is 1 ppm. Yes, too much fluroide can cause fluorosis, but no Fluoride increases risks for decay.
Flouride. Yes- you need to worry about your child swallowing flouride. Checkout the products at www.Carifree.Com for some safe alternatives.
Flouride . Flouride used topically (applied the exterior surface of the teeth) is wonderful for children and their teeth. The danger of too much flouride is only if they're swallowing it. If your child is old enough to be able to spit out all of the adult toothpaste after brushing and can avoid swallowing it, then it should be fine for them to use your toothpaste, they just might be sad it's not bubblegum flavored with their favorite cartoon character on the tube.
Yes. Young children can get to much Fluoride that can damage developing permanent teeth. They only need a small amount to keep their baby teeth healthy. Until they can reliably rinse and spit without swollowing they should use an infant toothpaste with no fluoride. Once they can reliably rinse and spit children and adults should use a pea sized amount of Fluoride toothpaste.