With all 4 I have nursed well past the 2 year period it is recommended to give them full fat milk. My 6 yo is still very sensitive to cows milk protein. He drinks rice milk now.
Once they are bigger they really only need to nurse a few times a day to get what they need.
In the second year (12-23 months), 448 mL of breastmilk provides:
29% of energy requirements
43% of protein requirements
36% of calcium requirements
75% of vitamin A requirements
76% of folate requirements
94% of vitamin B12 requirements
60% of vitamin C requirements
– Dewey 2001