Oral Motor

My son is 3.5 years old and has just begun speech therapy at a private clinic. The only areas of speech sound production/phonology that he struggles with are certain /s/ blends (sw and sp).

So he might say /fwim for swim/ or /fpoon for spoon/. Also he, reduces other cluster sounds, for example, /bed for bread/ or /pane for plane/.

He is able to imitate these at the word level fairly easily. My bigger concerns I think relates to oral motor. He is not able to blow bubbles, blow out birthday candles, give kisses because he cannot protrude his lips.

He does have a sensitive gag reflex and brushing teeth is a struggle. We have started using an electric tooth brush hoping this would give him some more input.

His language seems intact. He speaks in utterance 5-7 words in length and communicates for a variety of purposes (requests, protests, comments, etc.)

What can I do to help him with oral motor skills? I am concerned this will make it difficult in the future to produce sounds such as /sh/ /ch/ and /r/.

Do you have any idea what might be causing the difficulty protruding his lips? Thank you for your help!