Looking for ideas on an extra long-term investment account for our kids

My wife and I have two kids (ages 6 and 3). We contribute enough to both of their RESPs each year to receive the full CESG grant. We’re now thinking about saving some additional money for each of them beyond the RESP over the next 15–20 years. Most of our own investments are in TD e-Series following the Canadian Couch Potato model, and the RESPs are invested the same way. We’re considering either: Wealthsimple + XEQT with automatic recurring purchases. TD + TEQT (commission-free), although I’d h