Last year, I made less than 10,000 by babysitting. I filled out a City Wage Earner Return (RD-109) and am not sure how to access that form online again or if it is needed

You can file a Kansas City Wage Earner Return in the Missouri interview.

Go through the Missouri interview until you see a screen with the heading "Kansas City Wage Earner Return Earnings Tax". Check the box and continue.

Note that this return is only for employees (wage earners) and not the self-employed.

The self-employed (as I assume a babysitter is) should file a Kansas City Profits Return (RD-108). If this applies to you, then continue in the Missouri interview until you see the screen with the heading "Kansas City Profits Return Earnings Tax" and check the box on this screen instead. Continue the interview.

You can read about RD-108 here at the City website.