What to do when your toddler doesn't want to use the car seat at all?

Initially do not push him too much and you can be by his side but eventually teach him why it is important for him to sit on the car seat. Show him some videos sitting in ghe car seat and let him know how you appreciate him sitting in the car seat. You can treat him if he does that. Appreciate him front of family members snd his friends about this. I am sure, he will get used to it. Just keep encouraging him and appreciate him when he sits in the car seat.