'Swim to me' is an order and would be said 'snámh chugam'. 'Snámhann tú chugam' is in the habitual tense.
LOL, I read it in English, and thought that it was supposed to be an order. Like "You over there! Swim to me!" I guess I just misunderstood what the English sentence was trying to convey.
So, in essence, this could be said whenever those damn kids just won't stop swimming to you?
In Irish the verb would have a different suffix, or none in the command /imperative form The suffix -ann signals pres habitual tense
Snámhann tú / you swim (on a recurring basis)
Tá tú ag snámh / you are swimming (at this very moment)