other rules about cognates :
Most words ending in 'ion' are the same in English and spanish...
education = educación (etc)
words ending in 'dad' are 'ity' wirds in English :
universidad = university
Ciudad = City
words ending in 'ble' are the same...
possible = posible
words ending in 'rio' are 'ry'
accsesorio = accessory
There are many more too...
If you don't know it, guess! Half the time you'll be right... and the rest of the time they'll know what you're trying to get at and correct you
Another point I'd add to Synchronicity's post, is that adults have the ability to make the above type of connection, whereas children don't... they just learn by 'immersion' and off pat. Adults tend to be able to work something out, but children don't know it if they haven't learnt it.