New to all this?
Start with the whole Parent Play Style hub for everything in this cluster.
See the hubNo, don't secretly let them win by missing on purpose. Yes, handicap the contest itself.
Change the goal size, mark off a zone you can't leave, or give a head start, so a genuine result is possible either way. That difference matters more than the headline question of whether you should let your child win at football games. For a long time my idea of "going easy" was just missing on purpose, and I noticed my son got quietly better at spotting it than I was at hiding it, which told me the method, not the instinct, was wrong.

Letting kids win at games
The real issue with letting kids win at games is not whether it happens occasionally, it is what constantly rigging a result actually teaches. If a child wins every time because a parent is quietly missing saves or fluffing tackles on purpose, the lesson underneath is that outcomes get decided by someone else, not by anything the child actually did.
That is a worse lesson than losing fairly sometimes. A child who never has to earn a result has no way of knowing what earning one even feels like, and no way of trusting a win when it does happen. The question worth asking is not "should they win", it's how the contest itself is set up.
Handicapping football for a young child
Handicapping football for a young child means changing the shape of the contest, not faking what happens inside it. There are three reliable ways to do that, and none of them involve pretending. Rule-bending is the opposite problem, and if it is your child doing it, there is a page on what to do when a child cheats at football games.
A bigger goal for them, a smaller one for you. This changes the odds, not the honesty of each attempt. Every shot still has to be struck properly and every save still has to be a real save, the target sizes are just different.
A head start on the ball. A real advantage that still has to be finished properly. Starting closer to goal or a stride ahead gives a genuine edge, but the run still has to be made and the finish still has to land.
A marked zone you can't leave. Confining the defending parent to a small marked area in front of goal, rather than letting them roam and cover the whole pitch, hands the child room to work in everywhere else. A fair contest becomes genuinely possible without either of you faking anything, because the geometry is doing the work instead of a hidden decision.
One study, honestly hedged
65 children aged 4 to 6 played either cooperative or competitive board games over six weeks. Children enjoyed the cooperative games more, and playing competitive games made them compete more afterwards. But which type of game they played did not change how cooperative or prosocial they were overall (a study of cooperative and competitive games in young children, Eriksson, Kenward, Poom & Stenberg, 2021). The takeaway is that how a game is structured shapes what a child enjoys and how they behave afterwards.
This study used board games with children aged 4 to 6, not physical football in a garden, so it shows how game structure affects enjoyment and behaviour in a related but different context, not proof of identical effects in a garden kickabout.
See how Our Kickabout researches its pages.
Does losing on purpose help a child
A child who spots a rigged result and says so is not being ungrateful, they are correctly reading that something is off. Children notice patterns, and a parent who is always somehow just missing at the key moment is a pattern eventually.
The fix is not hiding it better. It's switching to a visible, named handicap they can see and understand, a bigger goal, a head start, a marked zone you can't leave. Once the handicap is out in the open, a genuine result stops needing to be a secret in the first place.

Quick answers
Not by secretly missing on purpose. Handicap the contest instead, a bigger goal, a head start, so a genuine win is actually possible.
If it is because you are quietly rigging it, yes, that catches up with both of you. If a genuine handicap is in place but they are still winning every time, that is a sign the handicap needs adjusting, a smaller goal for them or a shorter head start, until an occasional real win either way is actually possible.
Aim for a genuinely close, fair contest rather than a scoreboard target. Some evenings that means they win most rounds, some it doesn't, and that's fine too.
Keep going
Three places to go next, depending on what your evening actually needs.
Start with the whole Parent Play Style hub for everything in this cluster.
See the hubChild Upset Losing Football covers the in-the-moment reaction, whoever wins.
Read that pageNo-Elimination Football Games sidesteps the whole question with a different kind of contest.
See the gamesTonight's five minutes
One visible handicap beats a dozen quiet missed saves.