"geoaxes" cannot be the child of subplot. But we can set its position as follows (2x2 grid for example):
for i=1:2
for j=1:2
gx(i) = geoaxes('Position', [0.05+(j-1)*0.5 0.05+(i-1)*0.5 0.45 0.45]);
lat = rand(10,1)*180 -90;
lon = rand(10,1)*360;
geoplot(gx(i), lat, lon);
end
end