Say there first proper word?
Put 2 words together
Start forming full sentences.
Do all/any of the above clearly enough for everyone else to understand them?
For me -
Proper word - DS1 - 15 months, DS2 - 13 months,
2 word together - DS1 - 24 months, DS2 - just starting to now (21 months) (that's not including phrases he's learned as 'one word' (ie "Get off" or "Sit down").
Full sentences - DS1 25 months, DS2 - not there yet
Clearly for everyone else to understand - DS1 - 25 months, DS2 - single words about 15 months, 2 words together - 21 months, sentences.......still waiting