Nobody has actually studied this

Most clubfoot is isolated, also called idiopathic: it happens on its own, in a baby who is otherwise developing typically, and nothing else is found.4 That is the large majority of cases and the situation most parents reading this are in.

Syndromic clubfoot is different. Here the foot is one feature of a broader condition, such as arthrogryposis or a chromosomal difference, and other systems are involved because the same underlying cause reached them too.3

That distinction carries almost all the weight in this question. The only published papers that mention clubfoot and autism spectrum disorder in the same abstract are case reports of specific genetic abnormalities. In those children a single genetic cause produced features in several systems at once. It is a syndrome showing up in more than one place. It is not a foot doing something to a brain, and it says nothing about a baby whose clubfoot is isolated.

The larger study found more delay

A South Korean national cohort followed 484 children with idiopathic clubfoot against 4,840 matched controls, screening six developmental domains between 42 and 71 months. It reported an increased rate of neurodevelopmental delay and slightly reduced height, and concluded that monitoring is worthwhile.1

One number in it matters more than the headline. Premature birth was roughly twice as common in the clubfoot group, at 7.44% against 3.66%.1 Prematurity is an established risk factor for developmental delay in its own right, so part of what that study measured may be prematurity rather than clubfoot. A matched cohort can control for the things it matches on and not for the things it does not.

The better-designed study found nothing

A twin study compared 13 children who had clubfoot against their own twins who did not, across five developmental domains.2 That design is powerful, because a twin shares the genetics and the household, so a difference between them is harder to explain away. It found no significant difference in any domain, and no consistent direction favoring either child.

Thirteen pairs is a very small sample, small enough that a real but modest difference could hide in it. The paper has also drawn published letters of disagreement and author replies, so it is being argued about rather than settled.

What that adds up to

A large study that cannot fully separate clubfoot from prematurity found an association. A small study that can separate clubfoot from genetics and household found none. That is an unresolved question, not a finding, and anyone presenting it as either “clubfoot causes developmental problems” or “clubfoot has no effect at all” has gone further than the evidence.

Some of it is toe-walking. Persistent toe-walking is something parents associate with autism, and it is also something a foot with residual equinus or a tight heel cord does for entirely mechanical reasons. Two different causes producing a similar-looking gait is enough to start a search.

Some of it is the casting itself. A baby in casts for months moves differently, crawls later in some cases, and hits motor milestones on a slightly different schedule. That is a temporary consequence of having legs in plaster, and it resolves. Milestones are covered on when clubfoot babies walk.

And some of it is simply that a diagnosis at birth makes parents alert to everything else, which is a reasonable response and not a symptom of anything.

Raise development on its own terms. If something about how your child communicates, plays or responds is bothering you, that is worth taking to your pediatrician directly, not routed through the foot. The answer will be better because the question is the real one.

Nothing extra is indicated because of clubfoot alone. Routine developmental surveillance already happens at well-child visits. Isolated clubfoot is not a reason to add screening, and it is not a reason to skip it either.

Ask whether the clubfoot is isolated, and expect a real answer. Whether anything else was found is the single most consequential thing about a clubfoot diagnosis, and your team will have formed a view. It is also the question that resolves most of this page for your particular child. Related territory sits on whether babies with clubfoot have other problems and what causes syndromic clubfoot.