When you get told to play with Legos for a day, it's not an opportunity to be missed.
I recently spent a bit of time building a new member of Lego's Speed Champions set, a 1968 Ford Mustang fastback decked out in racing livery. For $14.99, you get 183 pieces, a bunch of stickers and a minifigure driver decked out in a racing suit.
The age range is 7 to 14 on the box, but enthusiasts will probably consider that to be an upper limit. Even if a little one is in charge of the build, some of those stickers are properly tricky to get aligned, so some adult oversight might be necessary if you want pitch-perfect decal placement. Building the 1968 Fastback took me about half an hour, and I have built... an embarrassing number of Lego sets in my thirties.
Ford has a number of Speed Champions sets, which relies on traditional Lego bricks. You can scoop up a Ford GT40, GT, F-150 Raptor, Fiesta WRC rally car and a 2015 Mustang, as well. If you want a bit more challenge, look to the Technic sets, which are geared toward older buyers and can get egregiously expensive -- the has 3,599 pieces and should cost between $300 and $400.
It might not be a recreation of the Mustang Bullitt, also a 1968 fastback in a very similar shade of green that just so happened toright around the time of this kit's release, but it's still a fun kit to put together and either leave on your shelf or roll around the house. Just make sure not to step on it -- it's one of the worst pains known to man.