My 4 month old daughter has recently started sucking her thumb, its her favourite passtime now. Dont know what ot do, as it irritates me like hell. I know its self soothing, but is it advisable, what if they carry the habit in their toddler hood, when do we stop them sucking.....very confused. She used to sleep on her own, no problems, but now she wants her thumb. Any suggesstions