We have tried a few rigs out over the years with our daughter,
The most success we have had is with the Ezzy Kids Rig, simply because of how light it is.
This rig comes with everything, 2.0 2.5 sails, as well as mast and base and boom, as well as a cool bag. Super easy to rig. great in light wind and maybe a 12 knot gusty day as well. Do not use in waves, we broke a mast one day in the shore break, it is only aluminium, so is fragile.
Phoebe has also sailed Hotsails Maui sails (microfreak and super freak), these are great sails, especially when they get into the 2.5, 3.0 sizes. The micro freaks are colourful, fun and also come with everything included. These sails are super strong and can take a pounding.
Phoebe has now graduated to a Severne S1. Ben makes some great smaller sails, which are the same construction I believe as the adult S1's. We were helped out with a boom and a mast, as these are harder to source. Phoebe is loving this sail, and is now looking at the harness (with some reservation as she is scared of catapulting) as she is planning around most days there is wind,
We also grabbed a second hand board, a 115 young gun, soft deck and good placed foot straps, this board is great to get on the plane quickly and is very comfortable, can also drift around when conditions are light, I reckon I could sail on it as well in the right conditions.
Phoebe also uses a starby SUP when its light and just wants to cruise around,
Phil, keep an eye out for the kids rigs, coz they do come up from time to time, from memory the ezzy kids rig was $380?
The NP Fly kids rigs are pretty cool too