I'm going to disagree with MsPeacock on the cheap bike idea. My suggestion is to find a garage sale bike, or buy a cheap Target / Walmart / General Tire bicycle. I'm meaning less than $150. There is also usually some "crazy Bike guy" in every county that has a fixation for bicycles and at anytime probably has 40+ bikes for sale out of his house / yard. - Yes you need several speeds if your area is hilly, but a 21 speed bike [ which seems to be the default anymore ] is likely more than you need.
Reason for disagreeing on the expensive bicycle is this -- The absolute cheapest i saw listed in Ms Peacocks links was about $600, most were above $1000, if not $2000+ . Yes, do not expect a $100 Walmart bike to last for 10 years. But jumping right into this with a $1000 bike seems overkill. MAybe it turns out you don't like riding that much. You'll find cycling up a steep hill is way harder than walking up it. MAybe there are no bicycle lanes in your town, maybe you find out you are not comfortable riding next to to 4500lb vehicles blasting past you at 50mph, 2 feet away, by yourself, to say nothing of adding a child into the danger zone.... * Jumping right in with a $1000+ plus bike would be like never having bowled before -but buying a custom cut, custom colored, balanced and polished bowling ball for big $$
Someone in your circle of friends / acquaintences will Lend you a bicycle to learn on. That is free.
If it turns out you like bicycle riding for errands and general transportation, then give away / donate, the cheap garage sale/ Walmart bike , and than buy a nice one.
edit to add - once your child turns about 5 years old, they are going to want their own bicycle and not be pulled around in mommy's cart.