So unless it was someone in the family, or someone who had access to the land, it can't be a kidnapping...
According to AI Overview. "Four-year-olds may wander from home to explore, to reach a desired location or item, or to escape a stressful situation like loud noises or demands at school."
While AI Overview isn't always correct. I suspect that the child must've had a reason to leave home...
For example, if it was a kidnapping, some random guy in the bushes offering free candy or something...
I'd say the most likely reasons would be to explore or to escape a stressful situation, with the latter only possible if the family has had fights in recent days.