So I'm not really sure which circle this belongs too, so let me know if it fits better somewhere else.
My younger kids are wishing a kareokee machine for their birthdays...but I couldn't really get myself to buy one of those cheap looking poor sounding machines. We had an older cheap battery powered one before and it was painful to listen to. So I will put together my own instead and make it so it will function more like a simple PA with a mixer instead so we also can use it for some instruments (keyboard, guitarr) plus have a computer interface for effects, recording and mixing (which my older kids expressed an interest in)
I already have plenty of amps, and speakers that will work since it doesn't need to be moveable and big PA speakers will not pass WAF in the living room.
So I'm looking for some help on finding mic preamps, mixer, computer interface (and software) that are simple enough for kids to use and can handle some abuse (or not too expensive to replace if they break). Plus they can't be too big in size since I will put it in my own enclosures.
Any brands and models you would recommend? Sound just needs to be OK. - Problem free, high quality and ease of use is much higher on the priority scale than superior sound.
So to summarize:
2-3 mic inputs with mic preamps
2+ RCA inputs for music from cell phones, tablets, laptop, etc.
2+ inputs for keyboard, etc.
Unbalanced and balanced output to amp.
Plus USB computer interfaces
It's the computer interface where I get stuck. What do I need to be able to get real time effects with low latency? Is that out of reach for cheap and cheerful price levels? I have seen some mixers with USB outputs and even tried an older Presonus USB model, but that one didn't have all the inputs I need.
And if you haven't guessed it by now, this will partly be for me too

Any help and ideas would be much appeciated.