The next step is to prick them out. You have to loosen them from the growing medium, very carefully so as not to damage the roots, then, holding each one by the seed leaves, plant them up into trays. They should be 3-4 inches apart. They will soon grow big enough to go outside into the ground but they are too little yet.
It's often not necessary to multi-sow beet ... many types of beet seeds contain several embryos and are 'multi-germ' and will give rise to several plants which need thinning/singling.
Some modern varieties have been developed (particularly for commercial use) to be 'mono-germ' and will not require singling. Monogerm seeds were first developed for the sugar beet growing industry, negating the need for the labour intensive hand singling of my childhood.
Carrots don't usually respond well to being replanted, but Chantenay carrots are small and stumpy so you might get away with it ... but I'd plant them straight out into the garden bed rather than pots, so they don't have to be disturbed again. I'd plant them about five inches apart to avoid having to thin them out ... disturbing them by thinning can attract carrot fly.
“I am not lost, for I know where I am. But however, where I am may be lost.” Winnie the Pooh
Posts
https://charlesdowding.co.uk/multisowing/
Some modern varieties have been developed (particularly for commercial use) to be 'mono-germ' and will not require singling. Monogerm seeds were first developed for the sugar beet growing industry, negating the need for the labour intensive hand singling of my childhood.
https://www.dtbrownseeds.co.uk/Vegetable-Seeds-1/Monogerm_2/