All you need is a phone line! All phone lines have a constant flow of voltage, around 40-70 volts (up to 100 volts when it rings!), but you can't just plug stuff into it and expect it to work.
Children older than 5 and more than 40 pounds must ride in a booster seat until the child is 8 years old or is taller than 4 feet 9 inches. Anyone over the age of 8 must be protected by a safety belt.
There are a variety of booster seats on the market that accommodate children from 40 up to 80 pounds. Several models are weight-rated even higher. Parents should strongly consider using booster seats - even past the age of seven - until their child is tall enough to fit into adult safety belts properly.