As the program right now is speculation the UBI is generally applied to only adults, or persons in the age of majority.
I haven't looked into how many of the pilot programs were calculated but some actually provide a lesser amount to couples. So If you or I as an individual were to receive 13000 as a couple we may receive 21000.
That right there sounds prone to abuse and unfairness if applied to any significant extent outside of a limited experiment. Expect shitloads of "unmarried" or suddenly "divorced" couples claiming $13k each. Kids need to eat and go to school and can't earn for themselves.
The only way this could possibly work at least to some extent as a replacement for welfare without its accompanying bureaucracy is if it's straight $13k for everyone, not dependent on marital status or age limitations, but you would still need some government involvement to make sure that e.g. kids are not starving and people with disabilities or other issues have a fair chance. Unless we're disregarding all that as part of the whole welfare system, in which case we might as well cut the UBI off at the age of 65 and let them old-timers fend for themselves.