I am so glad to have found this thread!
My son was born at 35 weeks, 5lbs14oz (not bad for being so early!). He was a champion nurser and gained weight so quickly in the beginning- trippled his birth weight by 4months, deliciously chubby baby. He was up to 29lbs at 11 months (i don't know percentiles, we don't see a mainstream doctor). He (and I) have been dairy-free (except butter) since figuring out that he was casien-intollerant/allergic when he was about a month old, and he's gluten free after trying out wheat crackers at about 13 months and having a reaction. I minimize gluten in my own diet because it tends to make his eczema flare up. We've done baby-led weaning. He eats a huge variety of foods, but hardly any in terms of volume. Some days we're lucky to get a few blueberries and a bit of egg and a cracker into him. I make lots of bone broths and make fermented veggies and so on, but can't really get that good stuff into him. Though he absolutely LOVES rice, so I try to make rice in broth for him. Aaaannnyyyways, He is 20.5 months now, and 26 or 27 lbs. He doesn't look skinny to me, still has a little belly, but so much thinner than he used to be. He is a real boobie-boy, and nurses a lot, and through the night, be he is starting daycare full-time in 6 weeks and I am a bit concerned about that, where he won't have access to my milk. Hopefully he'll just start eating then? In the meantime I am going to try some of these ideas that you have posted! I think the smoothie will be a hit! And making rice in coconut milk would be an awesome way to get some extra fat in!
Just thought I'd add something here as well as give my thanks too for all the great suggestions.
We did baby-led weaning too which worked great until 13-14 months when the world just got too interesting to stop for food. She loves juice, raisins and sweet tastes but alot of times wouldn't touch my lovingly prepared, organic buffet of goodies. So we started doing those things I never thought I'd do following the BLW track. I'd spoon the food for her, play airplane, pretend to feed Daddy etc. And it worked. Spooning the food for her seems a bit like its going into unconscious eating(and a bit silly for an 18 month old who can feed hersself!) but I always say whats on the spoon and make sure she wants it. I think she eats about 75% more due to these tricks. Not at all what I had in mind. One thinks kids will stop whirling about, get hungry and want to eat but it doesn't always work that way. Good luck everyone else who's dealing with this!
OP, your post is SO familiar to me! You almost exactly described my son. I checked this book out of our LLL meeting and it has helped me SO much!
When DS went through this phase the trick for us was to give up on the idea of 3 meal times and let him graze. We left him a little snack tray (it was actually like one of those craft oragnizing trays and filled each box with things we felt were okay for him to have: granola, biscuits, dried fruit and veg, pretzels,annie's bunnies, popcorn etc and in the fridge we had sliced up fresh fruit, mini yogurt cups, and small (1/8 of a normal sandwich) butter and cheese sandwiches, and a sippy cup with pumped BM.
9 times out of ten he would eat the whole tray in a day. But try to get him to sit down with the family and eat three square meals and 2 snacks...forget it. Not a bit would go in him.