Hi there! I nursed both of my children, one to 14 months, and one to 17, then only gave them water to drink. We did not use any dairy milk, plant-based milks, or juice for beverages. You can continue with formula up to age two, which is the recommended age to quit nursing by the World Health Organisation. There is no human requirement for cow's milk, as you know. It's really a matter of making sure the little ones have enough calories. The
Forks Over Knives Family book touches on this.
If you really want to give liquid calories, I feel most confident in Westsoy soy milk - it's organic, non-GMO and has no additives or thickeners/emulsifiers. Your little one will not be stunted somehow or deficient if you chose to just wean to water. Around this time they start to become more active and start walking, and start losing that baby fat and lengthen. It's nothing to be concerned about, it's just what toddlers do!
My girls are 2 (almost 3) and 4 1/2. Just as a point of reference I'll give you an outline of a typical day's eating:
Breakfast - Cheerios with unsweetened vanilla almond milk, 1/2 cup blueberries
Morning snack - banana with peanut butter
Lunch - applesauce, peanut butter and jelly on whole wheat bread
Afternoon snack - homemade Popsicles (essentially just frozen smoothie in a Popsicle mold) and whole wheat crackers
Dinner - (this is what we had last night) lentil loaf with ketchup, greens with balsamic vinegar, roasted sweet potato
Just make sure that they get more of those higher nutrient density foods and you'll be fine! My kids think they are the luckiest people in the whole world because sometimes we'll have dinner that consists of no-oil fries, ketchup and chocolate smoothie.
Here are some links from PCRM:
http://www.pcrm.org/health/diets/vegdiets/vegetarian-diets-for-children-right-from-the-starthttp://www.pcrm.org/sites/default/files/pdfs/health/Nutrition_for_Kids.pdf