Are any of the moons bigger than the planets?
Yes, there is. Ganymede (Jupiter III) is a satellite of Jupiter and the largest moon in the Solar System. It is the seventh moon and third Galilean satellite outward from Jupiter. Completing an orbit in roughly seven days, Ganymede participates in a 1:2:4 orbital resonance with the moons Europa and Io, respectively. It has a diameter of 5,268 km (3,273 mi), 8% larger than that of the planet Mercury, but has only 45% of the latter's mass.
Ganymede and Titan, which are moons of Jupiter and Saturn respectively, are larger than the planet Mercury. These are the only moons larger than any planets in our solar system. It is also worth noting that Jupiter's moons Callisto, Io, and Europa; Earth's moon; and Neptune's moon Triton are larger than Pluto, but Pluto is no longer considered a planet.
Our Moon is generally rated at the large end of the scale. Most planetary moons (such as those around Mars) are smaller than ours. To find any moons bigger than ours, you generally have to go to Jupiter or Saturn, where you will find the biggest moons in the system like Ganymede, Callisto, and Titan.
Yes. Ganymede and Titan, which are moons of Jupiter and Saturn, are larger than the planet Mercury. Several other moons in the solar system, including our own moon, are larger than Pluto, which was formerly considered a planet. These moons would likely be considered planets if they had their own orbits around the sun.