Yes.
Please don't try to use Toys without starting a new game if it's the first time you've introduced Toys to your load order. A new game is required.
But why? How about I use a save cleaner tool? Or I use a really really early save? Or maybe I'm skilled in the art of perfect load orders so I can get away with it?
No, won't help. All myths. Start a new game.
This info applies to all mods with a plugin (esm or esp). It's not just about Toys. It's all about the golden rule.
Case 1: Upgrading
Sometimes a new game is needed when upgrading because the mod changed in a significant way and things will not be able to be referenced anymore, so it's a hard fail, no way to avoid. Thus far Toys has not needed a new game for that reason as we go the extra mile to avoid that. A major update someday may need it.
Case 2: Adding to Load Order for the first time
Other times it's a load order issue. For example, Toys is an ESM. If adding it for the first time to your Load Order, you can't put an ESM at the end of your load order so you have no choice but to break the Golden Rule (see Golden Rule). Thus you must start a new game. Even if you think you put the ESM at the end of the load order (some mod managers let you try), Skyrim will re-sort and force it to load before all ESPs when you load the game.
If you don't start a new game when its a requirement, expect:
Random, unpredictable problems, with any mod, but particularly with newly installed ones
Sometimes MCM not showing up, and/or the mod stops running at all (common for esm)
Difficulty in getting support since you will be asked to recreate the problem after starting a new game. The chance of a corrupt save must first be ruled out
"WHY" the Golden Rule
The golden rule is about only one thing... don't change the load order (LO). It matters the first time you load a save.
A changed LO is an incompatible LO if it does not match the LO in a save you load. If you use that incompatible LO, this makes your next save corrupt. A LO can only have changes where you added/removed at the end of the stack.
Example: You saved with this...
Slot 1 -esm1
Slot 2 -esm2
Slot 3 -esp1
Slot 4 -esp2
Following the golden rule...
Slot 1 -esm1
Slot 2 -esm2
Slot 3 -esp1
Slot 4 -esp2
Slot 5 -esp3 ADDED
BREAKING the golden rule...
Slot 1 -esm1
Slot 2 -esm3 (toys for example) ADDED
Slot 3 -esm2
Slot 4 -esp1
Slot 5 -esp2
In this breaking case, if mod esp1 was referencing esm2, it recorded that as in slot2. That's baked into the save. Now it will reference slot 2 but Toys is there instead. Corrupt save if you save it.