I was taught with a stick figure where 2 months was shoulder level, 4 months elbow, 6 months waist, 8 hips, 10 knees and 12 feet. the idea being that you get muscle control from top to bottom, so by two months you can control your neck, so you dont have head lag, by 4 you control your shoulders and can roll, by 6 sit if they put you in sitting position but not get there yourself, by 8 sit yourself (hip control) then obviously crawl and walk 10 and 12. 12 was also talk in single words. 2 yo talk in 2 word sentences 1/2 understandably, parallel play, can copy a line. 3 yo can do circular movements, draw a circle, ride a tricycle, walk up stairs with alternating feet, speak in 3 word sentences.