If you do it without the Teebike wheel, you can still do it with the Teebike wheel! It doesn't change the geometry or the safety of your bike. One very important point, however: make sure you check the perfect functioning of your brakes.
Also limit the total weight on the bike to 150kg
Note: the range of the wheel decreases according to the weight carried and the level of assistance. With a child seat, it will therefore be less important.