How do I train my 6-month-old into sitting in his high chair while eating? He becomes cranky at the middle of his feed so I end up feeding him on my lap

Babies, like most anyone, don't like change. To get your son accustomed to sitting in a high chair, I'd recommend the same strategy you've used to introduce anything to him at this point. For my daughter, the best way to get her acclimated to anything new was to just stay patient. He'll eventually ease into the concept of eating in his high chair if you just keep at it.

Just like anything else, it may help if you let your baby get used to things you want him to do. Please do it with consistency so he can get the pattern. If you want him to stay put in his high chair while feeding, continue doing so even if he's cranky at times. This will eventually turn into a part of his feeding routine if done continuously.

Persistency is key! Train him to get used to being in a high chair. Sooner or later he should get accustomed to it. On the other hand, however, make sure that there's nothing wrong with the high chair, that it's not uncomfortable or hurting your baby.