Bought a 16″ framed BMX bike for my kid, he’s now stepped up to a specialized 20″ RipRock. If I had to do it again I’d take a look at this Early Rider Belter 16″ https://earlyrider.com/collections/bikes/products/belter-16-trail. I have their trailer runner xl for my younger son and it’s awesome https://earlyrider.com/collections/bikes/products/trail-runner-xl.