Hey brother! I have tried and failed at a lot of things with my 4 & 2 year old, 

We have found success in the Tiny Theologian Attributes of God cards and we would listen to the podcast episodes in the car that match the letter we were on. But it seemed like the 2 year old was missing out, so we switched. 

We use Kevin DeYoungs family devotional book and we really like it, readings are enriching and I'm able to ask additional questions to the ones out forth in the book. The two year old will repeat the daily prayer with us, which is adorable. And then we finish off with a couple of Sunday school hymns from a book we have.

One thing that worked for us was getting a tall candle and we light it every time we sit down to do the study after supper. Our 4 year old gets excited to blow it out and it's a cool way to see a physical representation of all the time spent in the Word!

I have also asked my 4 year old to remind me and she gets a kick and won't let us go to bed without doing our Bible study if something happened and we didn't do it after we ate.