Splitter question

I bought a small (physically and power output) tube amp for my daughter and have been trying out different tubes and speaker inputs to see what I like best and to burn in for her. The amp has only one input source. I plan on buying her an inexpensive turntable since she loves playing records (which she calls VIN...ALL), but she also has a CD player. I came up with what I thought was a great idea, but it didn’t work!  I put a splitter in the amp’s input so I could plug in 2 sources and just play which one I wanted. With one source plugged in to the splitter it worked but as soon as I put the cable from the 2nd source in too the 1st source stopped working. 

Are splitters only good for output and won’t work for input?  If this is true is there a way for me to provide 2 sources in or will she just have to unplug the 1st source and then plug in the 2nd if she wants to change from CD to VIN...ALL?

Thanks for any input.