New to all this?
Start with the whole approach behind Confident Beginners.
See Confident BeginnersOrdinary glasses aren't built to survive a flying ball.
Playing football safely with glasses means proper impact-resistant sports eyewear, not the pair worn to school - the American Academy of Pediatrics is clear that regular glasses and sunglasses do not provide enough protection for sport. Proper eyewear can be fitted with a child's own prescription, and a few simple rules help in the meantime.
I assumed for a while that a strap to keep his glasses on his face was the whole answer, until I read that a strap alone only keeps them in place - it doesn't make the lenses and frame underneath any more impact-resistant.

Can my child wear glasses playing football?
Regular eyeglasses and sunglasses do not provide enough protection for sport (American Academy of Pediatrics, HealthyChildren.org), whatever a child already wears them for day to day - standard frames and lenses simply are not impact-tested the way proper sports eyewear is. Read the guidance on eye protection for sports.
This is US paediatric guidance rather than a UK source, and its "football" risk category is American football, a different, helmeted sport. The same guidance separately classes soccer as a moderate-risk sport, which is the figure this page relies on, and it still recommends protective eyewear at that risk level.
Football sports goggles for kids
Proper sports eyewear means impact-resistant polycarbonate lenses in a snug, wraparound frame held on with a strap, and it can be fitted with a child's own prescription rather than replacing it.
While you sort proper eyewear
Three simple rules cut the risk down while proper eyewear gets sorted: keep shots below head height near a glasses-wearing child, skip heading entirely, and check the frame fit before every session.
Skipping heading follows The FA's own guidance for training in the foundation phase, meaning primary-school-age children: no heading at all, whatever a child wears on their face. See The FA's heading guidance and our full guidance on heading the ball for the detail.

Making it routine, not a big deal
Most standard opticians in the UK offer a sports goggle fitting alongside a normal eye test, so it doesn't need to be its own separate outing. Treating it as routine, not a special occasion, keeps a child from feeling singled out for wearing glasses in the first place.
Quick answers
Not recommended - ordinary glasses and sunglasses aren't built to withstand a flying ball, per the American Academy of Pediatrics, whatever they're already worn for day to day.
A snug, wraparound impact-resistant goggle frame that can be fitted with a child's own prescription lenses, available from most standard opticians as an add-on to a normal eye test.
The same source classes soccer as moderate risk rather than the highest tier, but still recommends protective eyewear given how serious an untreated eye injury can be.
Keep going
Three places to go next, depending on what you're working on. If your child wears an eye patch as well as glasses, football with an eye patch for a lazy eye sets out a slower, softer game.
Start with the whole approach behind Confident Beginners.
See Confident BeginnersOur guidance on heading the ball, for any child, glasses or not.
See the heading guidanceGetting the ball size right matters too, at any age.
See ball sizingTonight's five minutes
Five minutes of gentle ground passes while proper eyewear gets sorted.