They indeed likely have more difficulty than Spanish, Italian and German kids who use much more regular spelling and phonetic rules.

However, English speaking kids are reported to have more difficulties, given English spelling extreme irregularity.

Excerpt from "Troubles dans l’apprentissage de la lecture, Anne-Marie Chartier s’entretient avec Franck Ramus."

À la fin de la première
année d’apprentissage de la lecture, les
enfants allemands, suédois, italiens, espagnols, grecs, font moins de 6 % d’erreurs
quand ils lisent des mots, alors que les
enfants français et danois en font presque
30 %, et les enfants anglais 67 % (c’est-à dire pour deux mots sur trois)

A metric that can help figuring out the difficulty of reading in a given language is the ratio between the phonemes (all different vowels and consonants a language uses) and the graphemes (all possible ways to write the phonemes).

An ideal language would have a ratio of 1 (strictly unambiguous phonetic writing). Esperanto, Serbo-Croatian and Finnish are there or very close to while French is poor (3.51) and English is trailing (5.22) : See https://en.wikipedia.org/wiki/Phonemic_orthography