Tax query is formed wrong. It also array of arrays(queries)
get_posts([
'meta_query' => [
[
'key' => 'country',
'value' => 'Japan',
'compare' => 'LIKE'
]
],
'tax_query' => [
[
'taxonomy' => 'category',
'field' => 'slug',
'terms' => ['kids']
]
]
]);
the array should look like this:
Array
(
[meta_query] => Array
(
[relation] => OR
[0] => Array
(
[0] => Array
(
[key] => country
[value] => Japan
[compare] => LIKE
)
)
)
[tax_query] => Array
(
[0] => Array
(
[taxonomy] => category
[field] => slug
[terms] => Array
(
[0] => kids
)
)
)
)