What is the best way to invest for my kids?

I have 2 sons age 3 and 10 and me and my wife just had a talk about not putting our two sons in debt in the future. We want to start investing now for their future so that when they are done school and enter into adult life, they have enough money to invest and used it for their first downpayment for a house, for their wedding or whatever other things they want to use it for. We want our kids to be a head once that time comes. Im already teaching my oldest to put away half of whatever money he receives from us or from family members.

We do have RESP for both of them and we intend to use it for them to go get a higher education whether it be trades or a degree and its non negotiable. I didnt graduate post seconday and I dont want them to go through what I went through. We are planning to invest for them until they graduate college or get into trades. We are planning to put 100 dollars a month for each of them and possible increase if we have extra money. What would be the best way to do it?