I'm not sure ham radio is the right choice for that application. My first thought would be FRS (Family Radio Service). No licensing or testing is required to use them

The radios are small hand held transceivers with 22 channels. The radios are $10-40 each.

A step up from FRS is GMRS (General Mobile Radio Service). It is similar to FRS, but had 30 channels (the 22 of FRS plus 8 more), higher power limits, and does require a licenses. GMRS users are allowed to talk with FRS users on their shared channels.

A GMRS license does not require any testing. You just fill out a form and pay a fee (around $85, I believe). It's good for 10 years.