These are both basic small amps. I call them practice amps in this range. meaning this is the sort of amp you use to practice in your room, not to use on stage. Both are a single small speaker with a low power amplifier.
How long has the kid been playing? Skilled or just enthusiastic? You might consider a "larger" amp, even a used one. I can get fun tones from the little 8" speaker, but like an 8" speaker in your stereo, it sounds nothing like a 12" speaker.
As to the amps themselves, the MArshall is more old school. It has two "channels", meaning you plug in the guitar and you can select either the clean sound or the distorted overdrive sound. It also has a small basic spring reverb. The Fender is more new school, it has one "channel" but within that are 24 presets, meaning sound variations from clean through distorted. It is easily programmed for playing. There are some digital effects, including reverb. A feature I like is the tap/touch button. If you use echo (as opposed to reverb) you can change the speed of the echos. In other words "bop.....bop.....bop.....bop" versus 'bop..bop..bop..bop" I like to match the speed of my echo with the beat of my song. You tap on the TAP button 2 or 3 times at the speed you want and the echo beat runs now at that speed. The Fender also includes a tuner feature as well as a USB interface. The Fender has a lot of features to play with.
So to me the Fender is a more interesting piece, though the Marshall is cool in its own way. The Fender has WAAAY more features, and it evens costs $10 less. Also I think the Fender warranty is better. Marshall also has a warranty, but having been an authorized repair shop for both brands (as well as many others) I provided warranty support for both companies. There are more Fender repair shops out there than Marshall, service is easier to find.
And it does cost more but the Peavey Vypyr VIP is a feature laden little amp as well.