I must admit that I unintentionally stumbled across the Pikler Triangle, but I was instantly impressed. For little people, it's a climbing platform... kids love it! You have probably seen several threads about it if you have ever joined any Facebook groups for parents of toddlers or particularly about Montessori / Waldorf parenting. It's also definitely one of the best presents for the first birthday of a boy!
The Pikler Triangle was founded over 100 years ago by Dr. Emmi Pikler, a Hungarian pediatrician. She claimed that the Pikler triangle should be discussed by children on their own terms. They should be able to do it freely if they can climb it. It can be used for children from 6 months of age to approx. He's 5 years old.
While everything can easily be bought, you could also build it yourself. Its construction is simple, so even with little woodworking experience it can be done. Although it might take you a few tries and good couple of hours. The best plans for DIY pikler triangles is this one & that one. It will cost you about $100-120 for dowels, screws and wood, but unless you have woodworking tools, you would have to purchase them as well. This includes Forstner bit to do the holes (technically, you can do it without the holes to rest the dowels on, but it’s more stable with them), sander and long clamps.