Highchair Battles: Try a Picnic!
I never want to be seen as minimizing a family's frustration by suggesting something will cure all their issues or completely fix a problem, so I'll start by saying that this suggestion may work for some, and not for others. However, this suggestion is a go-to for my families struggling with a child not wanting to sit in a highchair or a kid who loses it as soon as they are required to get into their chair at the table. Every once in a while, try a picnic. It can be anywhere, but I especially like the living room because it's very easy to get there :) and just odd enough that most kids are excited to join in. I have my daughter set up as she likes- she uses her blankets but if you're worried about mess, you can put down a plastic table cloth or sheet and she adds in her stuffed animal friends for fun. Then we sit and eat...usually she's nude, because, that's how my daughter rolls.
As with any picnic, it's ok for her to get up and move around, come back to the meal, and generally be silly. I mentally set a timer on our picnic of about 30 minutes so if she's being super silly and not eating I give her some warnings that meal will be up in "x" number of minutes so she knows if she wants to eat, she has to come back and finish up. Usually she stays put and eats but not always. When meal is over, she helps me clean up. If she eats, fabulous, if not, that's her choice but she doesn't get any other food afterwards. We practice this same principle at all meals though, so she is very used to it by now.
One big rule for parents: you have to be having fun at the picnic too- no stressing over mess or worrying about whether or not your child is eating fast enough. No checking your cell phone or yelling. The primary value of this suggestion is that it reduces a child's anxiety around a meal and increases fun which allows a child to tap into their natural hunger and drive to participate. (When a child is stressed or anxious, hunger drops or disappears and resistant behaviors prevail.) It also breaks the connection between anxiety/tantrums/resistance and mealtime which is often the child's habit at the table or in the highchair.
Yes, it gets messy. And yes, you have to be ok with your child not sitting still and being silly at a meal. But a few basic rules apply, as always. Your kiddo can't wander around the house with food- if she wants to eat and be a part of the picnic, she has to sit or at least stay on or right near the picnic blanket. Everyone should be having fun and acting like you do at a picnic. That's about it!