I wouldn't have said they're exactly comparable in that sense and i'm not sure the relevance they have to a child learning.
Legato is the way of making notes connected by ensuring there's no break between them.
Portato is more advanced method of making notes connected by the manner in which they're played, usually done so by adding a slight accent or pause to the notes. I'm pretty sure the most common identification of this is staccato notes under a slur.
They don't necessarily need to be played in a full legato manner and if anything are a little advanced for a child to be learning in my opinion, it requires a level of maturity in expression to understand how they're being connected.
Lastly, the technical difference is more notable on other instruments like stringed instruments rather than a piano, but can be achieved in a similar manner never the less.